TO COMPLETE!! Needs string validation!

MathMethods.cs

using System;

namespace Unit2_Calculator_AzuaraFonseca {
    class MathMethods {

      public void showMenu() {
        Console.WriteLine("|----------------------------------------------|");
        Console.WriteLine("| A: Addition                                  |");
        Console.WriteLine("| B: Substraction                              |");
        Console.WriteLine("| C: Multiplication                            |");
        Console.WriteLine("| D: Division                                  |");
        Console.WriteLine("| E: exit program                              |");
        Console.WriteLine("|----------------------------------------------|");
      }

      public void handleOption(string opt) {
        if (opt == "A" || opt == "a") {

            Console.WriteLine("Please enter the first number");
            string fNum = Console.ReadLine();
            Console.WriteLine("Please enter the second number");
            string sNum = Console.ReadLine();

            int k = 0;
            int l = 0;

            if (!Int32.TryParse(fNum, out k) || !Int32.TryParse(sNum, out l)) {
              throw new ArgumentException("Arguments are not numeric!");
            }; // the values are returned as strings.

            // the values are converted to ints
            int result = Convert.ToInt32(fNum) + Convert.ToInt32(sNum);

            Console.WriteLine("The sum of " + fNum + " + " + sNum + " = " + result + "  ");

        }
        else if (opt == "B" || opt == "b") {

            Console.WriteLine("Please enter the first number");
            string fNum = Console.ReadLine();
            Console.WriteLine("Please enter the second number");
            string sNum = Console.ReadLine();

            int k = 0;
            int l = 0;

            if (!Int32.TryParse(fNum, out k) || !Int32.TryParse(sNum, out l)) {
              throw new ArgumentException("Arguments are not numeric!");
            }; // the values are returned as strings.

            int result = Convert.ToInt32(fNum) - Convert.ToInt32(sNum);

            Console.WriteLine("The substraction of " + fNum + " - " + sNum + " = " + result + "  ");
        }
        else if (opt == "C" || opt == "c") {

            Console.WriteLine("Please enter the first number");
            string fNum = Console.ReadLine();
            Console.WriteLine("Please enter the second number");
            string sNum = Console.ReadLine();

            int k = 0;
            int l = 0;

            if (!Int32.TryParse(fNum, out k) || !Int32.TryParse(sNum, out l)) {
              throw new ArgumentException("Arguments are not numeric!");
            }; // the values are returned as strings.

            int result = Convert.ToInt32(fNum) * Convert.ToInt32(sNum);

            Console.WriteLine("The multiplication of " + fNum + " * " + sNum + " = " + result + "  ");

        }
        else if (opt == "D" || opt == "d") {

            Console.WriteLine("Please enter the first number");
            string fNum = Console.ReadLine();
            Console.WriteLine("Please enter the second number");
            string sNum = Console.ReadLine();

            int k = 0;
            int l = 0;

            if (!Int32.TryParse(fNum, out k) || !Int32.TryParse(sNum, out l)) {
              throw new ArgumentException("Arguments are not numeric!");
            }; // the values are returned as strings.

            int result = Convert.ToInt32(fNum) / Convert.ToInt32(sNum);

            Console.WriteLine("The division of " + fNum + " / " + sNum + " = " + result + "  ");

        }
        else {
            Console.WriteLine("Invalid Input. Please try again");

        }
      }
    }
}

Unit2_Calculator_AzuaraFonseca.cs

using static System.Console;
namespace Unit2_Calculator_AzuaraFonseca {
    class Program {
        static void Main(string[] args) {

            // Instantiate Class
            MathMethods m = new MathMethods();

            string option= "";

            do {

                m.showMenu();
                WriteLine("Please enter an option");
                option = ReadLine();
                m.handleOption(option);

            } while (option != "e" && option != "E");
        }
    }
}

Throws Exception if invalid input is submitted