using System;

class Program
{
    static void Main()
    {
        int T = int.Parse(Console.ReadLine());
        
        string[][] cases = new string[T][];
        
        int[] L = new int[T];
        int[] R = new int[T];
        int[] A = new int[T];
        int[] B = new int[T];
        
        
        for(int i=0; i<T; i++)
        {
            cases[i] = Console.ReadLine().Split(' ');
            L[i] = int.Parse(cases[i][0]);
            R[i] = int.Parse(cases[i][1]);
            A[i] = int.Parse(cases[i][2]);
            B[i] = int.Parse(cases[i][3]);
        }
        
        int[] Max = new int[T];
        
        for(int i=0; i<T; i++)
        {
            if(A[i] < 0)
            {
                Max[i] = A[i] * L[i] + B[i];
            }
            
            else
            {
                Max[i] = A[i] * R[i] + B[i];
            }
            Console.WriteLine(Max[i]);
        }
        
        
    }
}