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

typedef long long ll;
typedef unsigned long long ull;
#define N 10010
#define inf 1e18

int calc(int x)
{
    int ans = 0;
    while (x) {ans = max(ans, x % 10); x /= 10;}
    return ans;
}

void sol()
{
    int la, ra, lb, rb;
    cin >> la >> ra >> lb >> rb;
    if ((ra + rb) - (la + lb) >= 10) {cout << 9 << '\n'; return ;}

    int ans = -1;
    for (int i = la; i <= lb; i ++)
    {
        for (int j = ra; j <= rb; j ++)
        {
            ans = max(ans, calc(i + j));
        }
    }
    cout << ans << '\n';
}

int main()
{
    int T; cin >> T;
    while(T --)sol();
    return 0;
}