#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define INF32 2147483647
#define ALL(x) x.begin(), x.end()
vector<int> ddx = {0, 1, 0, -1, 1, 1, -1, -1};
vector<int> ddy = {1, 0, -1, 0, 1, -1, -1, 1};


int main() {
  int t;cin>>t;
  rep(i,t){
    int l,r,a,b;cin>>l>>r>>a >>b;
    if(a < 0){
      cout<< l * a + b <<endl;
    }else{
      cout<< r * a + b <<endl;
    }
  }
  return 0;
}