#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define fi first
#define se second
int main(){
    int t;
    cin >> t;
    for(int i = 0; i < t; ++i){
        int l, r, a, b;
        cin >> l >> r >> a >> b;
        cout << max(a * l + b, a * r + b) << endl;
    }
    return 0;
}