#include<bits/stdc++.h>
using namespace std;
using ll=long long;
using pii=pair<int,int>;

#define all(a) a.begin(),a.end()
#define pb push_back
#define sz(a) ((int)a.size())

signed main(){
    ios_base::sync_with_stdio(0),cin.tie(0);
    int t; cin >> t;
    while(t--){
        int l,r,a,b; cin >> l >> r >> a >> b;
        cout << max(a*l+b,a*r+b) << "\n";
    }
}