#include <iostream>
#include <vector>
#include <cmath>
#include <map>
#include <set>
#include <iomanip>
#include <queue>
#include <algorithm>
#include <numeric>
#include <deque>
#include <complex>
#include <cassert>

using namespace std;

void solve(){
    int L, R, A, B;
    cin >> L >> R >> A >> B;
    cout << max(A*L, A*R)+B << endl;
}

int main(){

    int T;
    cin >> T;
    while(T){
        solve();
        T--;
    }

    return 0;
}