#include<bits/stdc++.h>
using namespace std;
#include<atcoder/all>
using namespace atcoder;
using ll = long long;
ll l,r,a,b;
ll f(ll x){
	return a*x+b;
}

void solve(){
	cout<<max(f(l),f(r))<<endl;
}

signed main(){
	cin.tie(nullptr);
	ios::sync_with_stdio(false);
	ll t;
	cin >> t;
	while(t--){
		cin >> l  >> r >> a >> b;
	solve();
	}
}