#include <iostream>
using namespace std;

int main(){
    int T;
    cin >> T;
    while(T--){
        int L, R, A, B;
        cin >> L >> R >> A >> B;
        if (A >= 0){
            cout << R * A + B << endl;
        }
        else{
            cout << L * A + B << endl;
        }
    }
}