int main()
{
    int n, i, len1, len2, j, k, char11[101] = {0}, char22[101] = {0}, flag = 0, answer[101] = {0};
    char char1[101], char2[101];
    cin >> n;
    for (i = 1; i <= n; i++)
    {
        cin >> char1 >> char2;
        len1 = strlen(char1);
        len2 = strlen(char2);
        memset(answer,'\0',sizeof(answer));
        memset(char11,'\0',sizeof(char11));
        memset(char22,'\0',sizeof(char22));
        k = 0;
        for (j = len1 - 1; j >= 0; j--)
        {
            char11[k] = char1[j] - '0';
            k++;
        }
        k = 0;
        for (j = len2 - 1; j >= 0; j--)
        {
            char22[k] = char2[j] - '0';
            k++;
        }
        for (j = 0; j < len1; j++)
        {
            if (char11[j] < char22[j])
            {
                char11[j + 1] = char11[j + 1] - 1;
                answer[j] = char11[j] + 10 - char22[j];
            }
            else
            {
                answer[j] = char11[j] - char22[j];
            }
        }
        for (j = len1 - 1; j >= 0; j--)
        {
            if (answer[j] != 0)
            {
                flag = 1;
            }
            if (flag == 1)
            {
                cout << answer[j];
            }
        }
        cout << endl;
    }
    return 0;
}