#include <bits/stdc++.h>

using namespace std;
void fast_io() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
}

int main() {
    fast_io();
    int t;
    cin >> t;
    for (; t--;) {
        int l, r, a, b;
        cin >> l >> r >> a >> b;
        cout << max(a * l, a * r) + b << "\n";
    }
}