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

#define FOR(i, a, b) for (int i=(a); i<(b); i++)
#define FORD(i, a, b) for (int i=(a); i>(b); i--)
#define ALL(w) w.begin(), w.end()
#define SZ(x) ((int)(x).size())
#define pb push_back

void solve()
{
	int p0, pw, v0, vw;
	scanf ("%d%d%d%d", &p0, &pw, &v0, &vw);
	
	int dw = abs(p0 - pw) + p0;
	
	long long res0 = 1ll * p0 * v0;
	long long resw = 1ll * dw * vw;
	
	printf("%lld\n", min(res0, resw));
}

int main()
{
	int t;
	scanf ("%d", &t);
	while (t--)
		solve();
	return 0;
}