/* -*- coding: utf-8 -*-
 *
 * 2208.cc:  No.2208 Linear Function - yukicoder
 */

#include<cstdio>
#include<algorithm>
 
using namespace std;

/* constant */

/* typedef */

/* global variables */

/* subroutines */

/* main */

int main() {
  int tn;
  scanf("%d", &tn);

  while (tn--) {
    int l, r, a, b;
    scanf("%d%d%d%d", &l, &r, &a, &b);

    printf("%d\n", max(a * l + b, a * r + b));
  }

  return 0;
}