#include<bits/stdc++.h>
using namespace std;


int main() {
	int T;
	cin >> T;

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