using static System.Math;
using System.Collections.Generic;
using System.Linq;
using System;

public class Hello
{
    static void Main()
    {
        var t = int.Parse(Console.ReadLine().Trim());
        while (t-- > 0)
        {
            string[] line = Console.ReadLine().Trim().Split(' ');
            var L = int.Parse(line[0]);
            var r = int.Parse(line[1]);
            var a = int.Parse(line[2]);
            var b = int.Parse(line[3]);
            getAns(L, r, a, b);
        }
    }
    static void getAns(int L, int r, int a, int b)
    {
        var ans1 = L * a + b;
        var ans2 = r * a + b;
        Console.WriteLine(Max(ans1, ans2));
    }
}