#include<stdio.h>
void solve()
{
	int l, r, a, b;
	scanf("%d %d %d %d", &l, &r, &a, &b);
	int ans;
	if (a < 0)
		ans = a * l + b;
	else
		ans = a * r + b;
	printf("%d\n", ans);
	return;
}
int main()
{
	int t;
	scanf("%d", &t);
	for (; t > 0; t--)
		solve();
	return 0;
}