#pragma GCC target("avx")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>
using namespace std;
void solve() {
    int L, R, A, B;
    cin >> L >> R >> A >> B;
    cout << max(A*L+B, A*R+B) << endl;
}
int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    int t;
    cin >> t;
    while(t--) {
        solve();
    }
}