#include <iostream>
using namespace std;

int main(void){
	int T, L, R, A, B;
	int ans = 0;
	cin >> T;
	
	for (int i = 0; i < T; ++i){
		ans = 0;
		cin >> L >> R >> A >> B;
		if (A > 0){
			ans = A * R + B;
		}else if (A < 0){
			ans = A * L + B;
		}else{
			ans = B;
		}
		
		cout << ans << endl;
	}
	
	return 0;
}