CPE.11448

#include <bits/stdc++.h>

using namespace std;

void sol(string a, string b) {
    short aint[10001] = {0}, bint[10001] = {0}, result[10001] = {0};
    reverse(a.begin(), a.end());
    reverse(b.begin(), b.end());
    int aindex = 0, bindex = 0;
    for (auto it : a) {
        aint[aindex++] = it - '0';
    }
    for (auto it : b) {
        bint[bindex++] = it - '0';
    }
    aindex--;bindex--;
    bool flag = false;
    int resultLen = max(aindex, bindex);
    if (aindex <= bindex) {
        for (int i = resultLen; i >= 0; i--) {
            if (aint[i] != bint[i]) {
                flag = (aint[i] < bint[i]);
                cout << (flag ? "-" : "");
                break;
            }
        }
    }
    if (flag) {
        for (int i = 0; i <= bindex; i++) {
            result[i] = bint[i] - aint[i];
            if (result[i] < 0) {
                result[i] += 10;
                result[i++]--;
            }
        }
    } else {
        for (int i = 0; i <= aindex; i++) {
            result[i] += aint[i] - bint[i];
            if (result[i] < 0) {
                result[i] += 10;
                result[i + 1]--;
            }
        }
    }
    while(resultLen> 0&& !result[resultLen]) --resultLen;
    while(resultLen>=0) cout << result[resultLen--];

}

int main(int argc, char const *argv[]) {
    std::ios_base::sync_with_stdio(false);
    std::cin.tie(0);

    string a, b;
    int n;
    cin >> n;
    for(; n>0; n--){
        cin >> a >> b;
        sol(a, b);
        cout << endl;
    }

    return 0;
}