#include<bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i,m,n) for(int i=m; i<n; ++i)
#define repl(i,m,n) for(ll i=m; i<n; ++i)

int main(){
    int T;
    cin >> T;

    rep(i, 0, T){
        int L, R, A, B;
        cin >> L >> R >> A >> B;
        cout << max(L*A + B, R*A + B) << endl;
    }

    return 0;
}