#include <stdio.h>

int main () {
  int t = 0;
  int l = 0;
  int r = 0;
  int a = 0;
  int b = 0;
  
  int res = 0;
  
  res = scanf("%d", &t);
  while (t > 0) {
    res = scanf("%d", &l);
    res = scanf("%d", &r);
    res = scanf("%d", &a);
    res = scanf("%d", &b);
    if (a > 0) {
      printf("%d\n", a*r+b);
    } else {
      printf("%d\n", a*l+b);
    }
    t--;
  }
  
  return 0;
}