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]);
            Console.WriteLine(a >= 0 ? a * r + b : a * L + b);
        }
    }
}