#include <bits/stdc++.h>

using namespace std;

using ll = long long;
using ld = long double;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using vi = vector<int>;

#define pb push_back
#define eb emplace_back
#define fi first
#define se second
#define all(x) begin (x), end(x)
#define sz(x) (int) (x).size()
#define rep(i,a,b) for (int i = (a); i < (b); i++)

mt19937 rng(random_device{}());

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

	ll n;
	cin >> n;
	for(ll i = 0; i < n; i++){
		ll l, r, a, b;
		cin >> l >> r >> a >> b;
		if(a < 0){
			cout << (a * l) + b << endl;
		}else{
			cout << (a * r) + b << endl;
		}
	}

	return 0;
}