#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;
using ll = long long;

int main(){

    ll T, l, r, a, b;
    cin >> T;
    while(T){
        T--;
        cin >> l >> r >> a >> b;
        cout << max(a*l+b, a*r+b) << endl;
    }

    return 0;
}