#include <iostream>
using namespace std;
using ll = long long;
int main () {
    int T;
    cin >> T;
    for (int pk  =0; pk < T; pk ++) {
        ll l, r, a, b;
        cin >> l >> r >> a >> b;
        cout << max(a * l + b, a * r + b) << endl;
    }
}