#include <bits/stdc++.h>
using namespace std;


int cal(int x) {
    int res = 0;
    while (x > 0) {
        res = max(res, x % 10);
        x /= 10;
    }
    return res;
}
void solve() {
    int a, b, x, y;
    cin >> a >> b >> x >> y;
    if (max(b - a, y - x) >= 20) {
        cout << 9 << '\n';
    } else {
        int res = 0;
        for (int i = a; i <= b; i++) {
            for (int j = x; j <= y; j++) {
                res = max(res, cal(i + j));
            }
        }
        cout << res << '\n';
    }
}

int main() {
    ios_base::sync_with_stdio(false);

    int tt;
    cin >> tt;
    while (tt--) solve();

    return 0;
}