#include<iostream>
#include<string>
#include<cstring>
#include<algorithm>
#include<cmath>
using namespace std;
const int N = 1e4 + 10;
int a[N], b[N], c[N];

int main()
{
ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
int t;
cin >> t;
while (t--)
{
long long a, b, c, d;
cin >> a >> b >> c >> d;
long long x = a + c;
long long y = b + d;
if (y - x >= 10)
{
cout << 9 << endl;
}
else
{
int e = 0;
while (x <= y)
{
long long z = x;
while (z > 0)
{
int f = z % 10;
e = max(e, f);
z /= 10;
}
if (z >= 9)break;
x++;
}
cout << e << endl;
}
}

return 0;
}