#include <iostream>
#include <algorithm>
#include <vector>
#include <math.h>

using namespace std;

int main()
{
    int num_cases;
    cin >> num_cases;
    // uint64_t result = 0;

    for (int i = 0; i < num_cases; i++)
    {
        int my_floor, lift_floor, my_speed, lift_speed;
        cin >> my_floor >> lift_floor >> my_speed >> lift_speed;

        if (my_floor > lift_floor)
        {
            lift_floor += 2 * (my_floor - lift_floor);
        }
        if (my_floor * my_speed < lift_floor * lift_speed)
        {
            cout << my_floor * my_speed << "\n";
        }
        else
        {
            cout << lift_floor * lift_speed << "\n";    
        }
    }
    


    return 0;
}