#include <bits/stdc++.h>
using namespace std;
// #include<ext/pb_ds/assoc_container.hpp>
// #include<ext/pb_ds/tree_policy.hpp>
// #include<ext/pb_ds/tag_and_trait.hpp>
// using namespace __gnu_pbds;
// #include <boost/math/tools/minima.hpp>
// #include <boost/multiprecision/cpp_int.hpp>
// namespace mp = boost::multiprecision;
// #include <atcoder/all>
// using namespace atcoder;
// https://atcoder.github.io/ac-library/production/document_ja/
typedef long long int ll;
typedef long double ld;
const ll mod = 1e9+7;
const ll INF = 922337203685477580;
#define rep(i,n) for (ll i = 0; i < (n); ++i)
#define Rep(i,a,n) for (ll i = (a); i < (n); ++i)
#define All(a) (a).begin(),(a).end()
#define Pi acos(-1)
using V = vector<ll>;
using P = pair<ll,ll>;
vector<ll> dx = {1, 0, -1, 0, 1, 1, -1, -1};
vector<ll> dy = {0, 1, 0, -1, 1, -1, 1, -1};
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }
struct edge{ll to, cost;};
using graph = vector<vector<edge> >;
struct IoSetup {
  IoSetup() {
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);
    cout << setprecision(15) << fixed;
  }
} iosetup;
void printvec(vector<ll> a) {
  for(ll i = 0; i < a.size(); i++) {
    cout << a[i] << ' ';
  }
  cout << '\n';
}
void printgrid(vector<vector<ll>> g) {
  for (ll i = 0; i < g.size(); i++) {
    printvec(g[i]);
  }
}

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() {
  ll t;
  cin >> t;
  while (t--) {
    solve();
  }
}