#include <bits/stdc++.h>
using namespace std;
#define rep(i, l, r) for (int i = (int)(l); i < (int)(r); i++)
#define rrep(i, r, l) for (int i = (int)(r); i > (int)(l); i--)
#define all(a) (a).begin(), (a).end()
#define rall(a) (a).rbegin(), (a).rend()


void solve() {
    int l, r, a, b;
    cin >> l >> r >> a >> b;
    if (a == 0) {
        cout << b << '\n';
    } else if (a > 0) {
        cout << (a * r + b) << '\n';
    } else {
        cout << (a * l + b) << '\n';
    }
}

int main() {
    int t;
    cin >> t;
    while (t--) {
        solve();
    }
}