#include <bits/stdc++.h>

#define DEBUG if (0 )
#define COUT cout << "\e[36m"
#define VAR(v) " [\e[32m" << #v << "\e[36m=\e[91m" << v << "\e[36m] "
#define ENDL "\e[39m" << endl

using namespace std;

int k, n, ki;
vector<int> avec, bvec, used, orgavec, aeqb;

void clean()
{
    ki = 0;
    used.clear(); used.resize(n, 0);
    aeqb.clear(); aeqb.resize(n, 0);
}

vector<int> strtovec(const string& s)
{
    vector<int> ret(s.size());
    for (int i = 0; i < (int)s.size(); ++i)
    {
        ret[i] = s[i] - '0';
    }
    return ret;
}
template<typename T>
ostream& operator<<(ostream& out, const vector<T> v)
{
    out << " |";
    for (int i = 0; i < (int)v.size(); ++i)
    {
        out << v[i] << ((i == (int)v.size()-1)? "| " : ",");
    }
    return out;
}

int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    int z;
    cin >> z;
    while(z--)
    {
        DEBUG COUT << endl << "NXT TEST" << ENDL;

        string astr, bstr;
        cin >> astr >> bstr >> k;
        avec = strtovec(astr);
        bvec = strtovec(bstr);
        orgavec = avec;

        n = (int)avec.size();

        clean();
        DEBUG COUT << VAR(n) << VAR(k)<< endl << "A:" << avec << endl << "B:" << bvec << ENDL;

        for (int i = n-1; i >= 0; --i)
        {
            if(i == n-1)
            {
                aeqb[i] = ((avec[i] < bvec[i])? 0 : (avec[i] == bvec[i])? 1 : 2);
            }
            else
            {
                aeqb[i] = ((avec[i] < bvec[i])? 0 : (avec[i] == bvec[i])? aeqb[i+1] : 2);
            }
        }
        aeqb.push_back(1);
        DEBUG COUT << "AEQB: " << aeqb << ENDL;

        int lastnot0 = -1;
        int lasttolower = -1, lowerto = -1, wasitequal = -1; ///last able to lower
        int lasti = -1;
        bool impossible = 0;
        DEBUG COUT VAR(ki) << "PHASE I getting even" << ENDL;
        for (int i = 0; i < n && ki < k; ++i)
        {
            DEBUG COUT << VAR(i) << VAR(avec[i]) << VAR(bvec[i]);

            if(avec[i] != bvec[i])
            {
                if(bvec[i] > 0 && avec[i] != bvec[i] -1) ///LASTTOLOWER I
                {
                    lasttolower = i;
                    lowerto = avec[i]-1;
                    wasitequal = 1;
                }
                if(ki < k-1)
                {
                    DEBUG COUT << "just even it" <<ENDL;
                    ki++;
                    used[i] = 1;
                    avec[i] = bvec[i];
                    lasti = i;
                    if(ki == k-1)
                    {
                        DEBUG COUT << "ki = k-1" <<ENDL;
                        break;
                    }
                }
            }
            else
            {
                DEBUG COUT << "EQ" << ENDL;
                if(bvec[i] > 0)  ///LASTTOLOWER II
                {
                    lasttolower = i;
                    lowerto = bvec[i]-1;
                    wasitequal = 1;
                }
            }
            DEBUG COUT << VAR(i) << "A:" << avec << ENDL;
        }

        int exepti = n;
         DEBUG COUT << "A:" << avec << ENDL;
        if(ki == k-1)
        {
            DEBUG COUT VAR(ki) << "PHASE II the last K" << VAR(lasti) << ENDL;
            for(int i = lasti+1; i < n && ki < k; i++)
            {
                DEBUG COUT << VAR(i) << ENDL;
                if(avec[i] != bvec[i])
                {
                    DEBUG COUT << "not eq" << VAR(aeqb[i+1])<<  ENDL;
                    if(bvec[i] > 0 && avec[i] != bvec[i] -1) ///LASTTOLOWER I
                    {
                        lasttolower = i;
                        lowerto = avec[i]-1;
                        wasitequal = 1;
                    }
                    if(aeqb[i+1] == 2)
                    {
                        DEBUG COUT << "EXEPT OR LOWER IT, a>b"<< VAR(i) << ENDL;
                        if(bvec[i] != 0)
                        {
                            DEBUG COUT<< "last k found, lowering?" << ENDL;
                            if(orgavec[i] == bvec[i] -1)
                            {
                                DEBUG COUT << "changed my mind, going to phase III cause a == a-1" << ENDL;
                                exepti = i;
                                break;
                                /*ki+= ((orgavec[i] == bvec[i] -1)? 0 : 1);
                                avec[i] =bvec[i]-1;
                                used[i] = ((orgavec[i] == bvec[i] -1)? 0 : 1);*/
                            }
                            else
                            {
                                ki++;
                                avec[i] =bvec[i]-1;
                                used[i] = 1;
                            }


                        }
                        else
                        {
                            ///use lasttolower?
                            DEBUG COUT << "NOT ABLE TO END WITH ONE K" << VAR(i) << ENDL;
                            exepti = i;
                            break;
                        }
                    }
                    else
                    {
                        DEBUG COUT << "Escape OR LOWER IT, a<=b"<< VAR(i) << VAR(aeqb[i+1]) << ENDL;
                        if(aeqb[i+1] == 0)
                        {
                            DEBUG COUT << "last k found, getting even" << ENDL;
                            ki++;
                            avec[i] = bvec[i];
                            used[i] = 1;
                        }
                        else if(bvec[i] != 0 && avec[i] != bvec[i]-1)
                        {
                             DEBUG COUT<< "last k found, lowering" << ENDL;
                            ki++;
                            avec[i] = bvec[i]-1;
                            used[i] = i;
                        }
                        else if(0 && avec[i] > bvec[i]) ///LETS HOPE IF ITS IMPOSSIBLE NINERI WILL NOT BE FOUND
                        {
                            /*DEBUG COUT << "IMPOSSIBLE" << ENDL;
                            cout << "-1\n";
                            impossible = 1;
                            break;*/
                        }
                        else
                        {
                            DEBUG COUT << "NOT ABLE TO END WITH ONE K" << VAR(i) << ENDL;
                            exepti = i;
                            break;
                        }
                    }
                }
                else
                {
                    if(bvec[i] > 0)  ///LASTTOLOWER II
                    {
                        lasttolower = i;
                        lowerto = bvec[i]-1;
                        wasitequal = 1;
                    }
                }
            }
        }
        if(impossible)
            continue;
        DEBUG COUT << "A:" << avec << ENDL;
        DEBUG COUT << VAR(exepti) << ENDL;
        int minniner = 0, maxniner = 0, accniner = 0, nineri= -1;

        if(ki == k)
        {
            DEBUG COUT << "ANSWER FOUND after phase II" << ENDL;
            for(auto el : avec)
                cout << el;
            cout << "\n";
            continue;
        }
        int additki = 0;
        for(int i = n-1; i >= 0; i--)
        {
            if(i == n-1) DEBUG COUT VAR(ki) << "PHASE III looking for the niner" << ENDL;

            if(bvec[i] != 0)
            {
                accniner = maxniner + ((used[i] == 0)? ((orgavec[i] != bvec[i]-1)? 1 : 0) : ((orgavec[i] != bvec[i]-1)? 0 : -1));
                if(i <= exepti && ki+accniner >= k)
                {
                    nineri = i;
                    avec[i] = bvec[i] -1;
                    ki += ((used[i] == 0)? ((orgavec[i] != bvec[i]-1)? 1 : 0) : ((orgavec[i] != bvec[i]-1)? 0 : -1));
                    DEBUG COUT << "found nineri" << VAR(nineri) << VAR(avec[nineri]) << ENDL;
                    used[i] = ((orgavec[i] != bvec[i]-1)? 1 : 0);
                    break;
                }
                if(orgavec[i] ==bvec[i]-1 && bvec[i] > 1)
                {
                    accniner = maxniner + ((used[i] == 0)? 1 : 0);
                    if(i <= exepti && ki+accniner >= k)
                    {
                        nineri = i;
                        avec[i] = bvec[i] -2;
                        ki += ((used[i] == 0)? 1 : 0);
                        DEBUG COUT << "found nineri, that is lower" << VAR(nineri) << VAR(avec[nineri]) << ENDL;
                        used[i] = ((orgavec[i] != bvec[i]-1)? 1 : 0);
                        break;
                    }
                }

            }

            if(used[i] == 0)
            {
                maxniner++;
            }
            else
            {
                additki++;
                used[i] = 0;
                avec[i] = orgavec[i];
            }
        }
        ki -= additki;
        if(nineri == -1)
        {
            DEBUG COUT << "COULDNT FIND NINERI, -1" << ENDL;
            cout << "-1\n";
            continue;
        }
        DEBUG COUT << "A:" << avec << ENDL;
        DEBUG COUT << VAR(nineri) << VAR(maxniner) << ENDL;
        for(int i = nineri+1; i < n; i++)
        {
            if(i == nineri+1) DEBUG COUT VAR(ki) << "PHASE IV nineing" << ENDL;
            DEBUG COUT << VAR(i) << ENDL;
            if(ki < k || used[i] == 1)
            {
                avec[i] = 9;
                ki += ((used[i] == 0)? ((orgavec[i] != 9)? 1 : 0) : ((orgavec[i] != 9)? 0 : -1));
                used[i] = ((orgavec[i] != 9)? 1 : 0);
            }

        }
        DEBUG COUT << "A:" << avec << ENDL;
        for(int i = n-1; i > nineri && ki < k; i--)
        {
            if(i == n-1) DEBUG COUT VAR(ki) << "PHASE V 8ing" << ENDL;
            if(used[i] == 0)
            {
                avec[i] = 8;
                ki++;
            }
        }
        DEBUG COUT << "A:" << avec << ENDL;



        if(ki == k)
        {
            for(auto el : avec)
                cout << el;
            cout << "\n";
        }
        else
        {
            cout << "-1\n";
        }


    }
    return 0;
}