using System;
using static System.Console;
using System.Linq;
using System.Collections.Generic;
class Program
{
    static int NN => int.Parse(ReadLine());
    static int[] NList => ReadLine().Split().Select(int.Parse).ToArray();
    static int[] NMi => ReadLine().Split().Select(c => int.Parse(c) - 1).ToArray();
    static int[][] NMap(int n) => Enumerable.Repeat(0, n).Select(_ => NMi).ToArray();
    public static void Main()
    {
        Solve();
    }
    static void Solve()
    {
        var t = NN;
        var ans = new int[t];
        for (var u = 0; u < t; ++u)
        {
            var c = NList;
            var (l, r, a, b) = (c[0], c[1], c[2], c[3]);
            ans[u] = Math.Max(a * l + b, a * r + b);
        }
        WriteLine(string.Join("\n", ans));
    }
}