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

void solve(){
    long int L, R, A, B;
    cin >> L >> R >> A >> B;
    if(A > 0){
        int m = max(L, R);
        cout << (A * m + B) << endl;
    } else{
        int n = min(L, R);
        cout << (A * n + B) << endl;
    }
}

int main(){
    int n;
    cin >> n;
    for(int i = 0; i < n; i++)
        solve();
    return 0;
}