#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
  #include "settings/debug.cpp"
  #define _GLIBCXX_DEBUG
#else
  #define Debug(...) void(0)
#endif
using ll = long long;
#define rep(i, n) for (int i = 0; i < (n); ++i)

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

int main() {
  int t;
  cin >> t;
  while (t--) solve();
  return 0;
}