c# math square root. finding side of an area

Question

last question of my homework. please help. i am so confused i dont even know where to start. if you could put some comments for me to understand that will be great.

Develop a menu-driven program that inputs a number X and, at the user's option, finds the area of a square with side x [Area = x2] , the area of a circle with radius X [Area = 3.14 * x2] , or the area of an equilateral triangle with side x [Area = Sqrt(3) / 4 * X2] . Use a case structure to handle the user's menu choice. Use the Sqrt method in the C# Math library. Display an error message if an invalid menu option is selected

Answer 1

//Develop a menu-driven program that inputs a number X and, at the user’s option, 
//finds the area of a square with side x [Area = x2], the area of a circle with radius X [Area = 3.14 * x2],
//or the area of an equilateral triangle with side x [Area = Sqrt(3) / 4 * X2]. 
//Use a case structure to handle the user’s menu choice. Use the Sqrt method in the C# Math library.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            int a = 0;
            double b = 0;

            Console.Write("Enter 1 for Area of square :\nEnter 2 For Area of Circle :\nEnter 3 for Equilateral Triangle :\n\n");
            aa:
            a = int.Parse(Console.ReadLine());

            switch (a)
            {
                case 1: 
                    Console.Write("\n\nEnter the Value of Side x : ");
                    b = double.Parse(Console.ReadLine());
                    double area = b * b;
                    Console.Write("\n\nThe area of square is {0}",area);
                    break;

                case 2:
                     Console.Write("\n\nEnter the Value of Side x : ");
                    b = double.Parse(Console.ReadLine());
                    double circle = (3.14) * (Math.Pow(b, 2));
                    Console.Write("\n\nThe Area of Circle is {0}",circle);
                    break;

                case 3:
                     Console.Write("\n\nEnter the Value of Side x : ");
                    b = double.Parse(Console.ReadLine());
                    double triangle = ((Math.Sqrt(3)) / 4) * (Math.Pow(b, 2));
                    Console.Write("\n\nThe Area of Triangle is {0}",triangle);
                    break;

                default:
                    Console.Write("\n\nEnter Correct Number : ");
                    goto aa;                    
            }
            Console.Read();
        }
    }
}