#include <bits/stdc++.h>
#define FOR(i, n) for(int i = 0; i < (n); ++i)
#define REP(i, a, b) for(int i = (a); i < (b); ++i)
#define TRAV(i, a) for(auto &i : (a))
#define SZ(x) ((int)(x).size())
#define X first
#define Y second
#define PR std::pair
#define MP std::make_pair
typedef long long ll;
typedef std::vector<int> VI;
typedef std::pair<int, int> PII;

constexpr ll INF = 1000000666ll*1000000666ll;

void solve(){
	ll yp, lp, ys, ls;
	std::cin >> yp >> lp >> ys >> ls;

	ll nogi = yp * ys;

	ll winda;
	if(yp < lp){
		winda = lp * ls;
	}else{
		winda = (2*yp-lp) * ls;
	}

	ll podejde = std::abs(yp-lp) * ys + lp * ls;

	std::cout << std::min(podejde, std::min(nogi, winda)) << "\n";
}

int main(){
	std::ios_base::sync_with_stdio(false);
	std::cin.tie(0);

	int t;
	std::cin >> t;
	while(t--) solve();

	return 0;
}