#include <bits/stdc++.h>

using namespace std;

void solve(){
	int l, r, a, b;
	cin >> l >> r >> a >> b;
	if(a >= 0)
		cout << (a * r) + b << endl;
	else
		cout << (a * l) + b << endl;
}

int main() {
	cin.tie(0)->sync_with_stdio(0);
	int t;
	cin >> t;
	for(int i = 0; i < t; i++)
		solve();
}