#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll=long long;
using ld=long double;
ll inf=10010010010010010;
ll mod=998244353;
int main(){
    ll t;
    cin >> t;
    for (ll o = 0; o < t; o++)
    {
        ll l,r,a,b;
        cin >> l >> r >> a >> b;
        cout << max(a*l+b,a*r+b) << endl;
    }
    
}