#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef string str;
int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0); cout.tie(0);
    ll t;
    cin >> t;
    cout << fixed << setprecision(0);
    while (t--)
    {
        ll l, r, a, b;
        cin >> l >> r >> a >> b;
        cout << max(l * a + b, r * a + b) << "\n";
    }
    return 0;
}