#include <bits/stdc++.h>
using namespace std;
using ll = long long;

#define overload3(_1, _2, _3, name, ...) name
#define rep1(n) for(ll _ = 0; _ < (n); ++_)
#define rep2(i, n) for(ll i = 0; i < (n); ++i)
#define rep3(i, a, b) for(ll i = (a); i < (b); ++i)
#define rep(...) overload3(__VA_ARGS__, rep3, rep2, rep1)(__VA_ARGS__)

#define all(x) (x).begin(), (x).end()
template <class T> using vec = vector<T>;

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    int T;
    cin >> T;
    rep(T){
        int L, R, A, B;
        cin >> L >> R >> A >> B;
        if(A >= 0) cout << R * A + B << "\n";
        else cout << L * A + B << "\n";
    }
}