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

int t;
int la, ra, lb, rb;

signed main() {
    ios::sync_with_stdio(0), cin.tie(0);
    cin >> t;
    while(t--) {
        cin >> la >> ra >> lb >> rb;
        int min = la + lb;
        int max = ra + rb;

        if (max - min >= 10) {
            cout << 9 << '\n';
        } else {
            int answer = -1;
            for (int i = min; i <= max; i++) {
                int j = i;
                while (j > 0) {
                    int temp = i % 10;
                    if (temp > answer) answer = temp;
                    j /= 10;
                }
            }
            cout << answer << '\n';
        }
    }
}