VGTU_ACM_ICPC_C

// VGTU ACM ICPC selection C
#include <iostream>
using namespace std;
long long int ggg;
long long int n, x;
long long int pages(long long int nd, long long int first)
{
    long long int tenpow = 1;
    int ndig = 0;
    long long int t = first;
    while(t > 0)
    {
        t = t/10; // 10
        tenpow *= 10;
        ndig += 1;
    }
    long long int sum = 0;
    long long int last = first - 1 + nd / ndig; // ndig
    while(last >= tenpow)
    {
        sum += tenpow - first;
        nd -= (tenpow - first) * ndig;
        first = tenpow;
        tenpow *= 10;
        ndig += 1;
        last = first - 1 + nd / ndig; // ndig
    }
    if(nd % ndig > 0)
    {
        return -1;
    }
    return sum + (last - first + 1);
}
int main()
{
    cin >> ggg;
    for(long long int i=0;i<ggg;i++)
    {
        cin >> n >> x;
        cout << pages(n, x) << endl; // n - nd, x - first
    }
    return 0;
}