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

int main(){
    int T;
    cin >> T;
    while(T--){
        ll l, r, a, b, mx = -(1ll << 60);
        cin >> l >> r >> a >> b;
        mx = max(mx, a * l + b);
        mx = max(mx, a * r + b);
        cout << mx << '\n';
    }
}