#include <bits/stdc++.h> 
using namespace std;
using ll =long long;
#define all(v) v.begin(),v.end()
 #define rep(i,a,b) for(int i=a;i<b;i++)
#define rrep(i,a,b) for(int i=a;i>=b;i--)

ll INF=2e18;

void solve() {


 ll L,R,A,B;cin>>L>>R>>A>>B;
 ll ans=-INF;
 ans=max(ans,A*R+B);
 ans=max(ans,A*L+B);

 cout<<ans<<endl;


}

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
    ll t;cin>>t;
    for(ll i=0;i<t;i++) {
        solve();
    }
}