#include <iostream>

using namespace std;

long int sizeAbs (long int n) {
    return n >= 0 ? n : -n;
}

int main() {
    long int cases;

    cin >> cases;

    for (long int i = 0; i < cases; i++) {
        long int personPos, liftPos, personSpeed, liftSpeed;
        cin >> personPos >> liftPos >> personSpeed >> liftSpeed;

        if (personSpeed <= liftSpeed) { //Osoba rychlejsi nez vytah
            cout << personPos * personSpeed << endl;
        } else {
            long int timeByLift = sizeAbs(personPos - liftPos) * liftSpeed + personPos * liftSpeed;
            long int timeByFoot = personPos * personSpeed;
            long int time3 = sizeAbs (personPos - liftPos) * personSpeed + liftPos * liftSpeed;

            cout << min (timeByFoot, min (timeByLift, time3)) << endl;
        }
    }
    return 0;
}