#include <cstdlib>
#include <iostream>
#include <string>
#include <sstream>
#include <bitset>

using namespace std;

static inline void reduceFirstZero(string& text)
{
    int counter = 0;

    while (text[counter] == '0')
    {
        counter++;
    }

    if (counter)
    {
        text = text.substr(counter, text.size());
    }
}

static inline const string hexCharToBin(char c)
{
    switch (c)
    {
    case '0': return "0000";
    case '1': return "0001";
    case '2': return "0010";
    case '3': return "0011";
    case '4': return "0100";
    case '5': return "0101";
    case '6': return "0110";
    case '7': return "0111";
    case '8': return "1000";
    case '9': return "1001";
    case 'A': return "1010";
    case 'B': return "1011";
    case 'C': return "1100";
    case 'D': return "1101";
    case 'E': return "1110";
    case 'F': return "1111";
    }
}

static inline string hexToBin(string hex)
{
    string binary;
    int hexl = hex.length();
    for (int i = 0; i < hexl; i++)
    {
        binary += hexCharToBin(hex[i]);
    }

    reduceFirstZero(binary);

    return binary;
}

static inline string binToHex(string block)
{
    stringstream ss;
    int blockl = block.length();
    for (int i = 0; i < blockl; i += 4)
    {
        bitset<4> set(block.substr(i,i+4));
        ss << hex << uppercase << set.to_ulong();
    }

    return ss.str();
}

static inline string textToBin(string text)
{
    string binary;
    int textl = text.length();
    for (int i = 0; i < textl; i++)
    {
        binary+=(bitset<8>(text.c_str()[i]).to_string());
    }

    reduceFirstZero(binary);

    return binary;
}

static inline string XOR(string first, string second, int size)
{
    string solution;

    for (int i = 0; i < size; i++)
    {
        (first[i] == second[i]) ? solution+='0' : solution+='1';
    }

    return solution;

}

static inline void crc(string& wx, string px)
{
    string tempRes;

    reduceFirstZero(wx);

    while (wx.length() >= px.length())
    {
        tempRes = XOR(wx, px, px.length());

        for (int i = 0; i < tempRes.length(); i++)
        {
            wx[i] = tempRes[i];
        }

        reduceFirstZero(wx);
    }

}

int main()
{
    int t,pxl;

    string text;
    string px;
    string wx;

    cin >> t;

    for (int i = 0; i < t; i++)
    {
        cin >> px >> text;
        px = hexToBin(px);
        wx = textToBin(text);
        pxl = px.length() - 1;
        for (int i = 0; i < pxl; i++)
        {
            wx += '0';
        }
        crc(wx, px);
        cout << binToHex(wx) << endl;
    }

    system("pause");
    return 0;
}