#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pll = pair<ll, ll>;
#define drep(i, cc, n) for (ll i = (cc); i <= (n); ++i)
#define rep(i, n) drep(i, 0, n - 1)
#define all(a) (a).begin(), (a).end()
#define pb push_back
#define fi first
#define se second

const ll MOD = 1000000007;
const ll MOD2 = 998244353;
const ll INF = 1LL << 60;
const ll MAX_N = 2e5;

void solve(){
    ll L, R, A, B;
    cin >> L >> R >> A >> B;

    if(A>=0){
        cout << A*R+B << "\n";
    }else{
        cout << A*L+B << "\n";
    }
}

int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    
    ll t;
    cin >> t;
    rep(i, t) solve();
}