#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using vll = vector<long long>;
using vvll = vector<vector<long long>>;
using vs = vector<string>;
#define lln \
  ll n;     \
  cin >> n;
#define REP(i, n) for (long long i = 0; i < n; i++)
#define REP2(i, s, e) for (long long i = s; i < e; i++)
#define UNIQUE_VECTOR(v) v.erase(unique(v.begin(), v.end()))
ll gcd(ll x, ll y) { return (x % y) ? gcd(y, x % y) : y; }
ll lcm(ll x, ll y) { return x / gcd(x, y) * y; }

int main() {
  ll t;
  cin >> t;
  REP(i, t) {
    ll l, r, a, b;
    cin >> l >> r >> a >> b;
    cout << a * ((a > 0) ? r : l) + b << endl;
  }
}