My 1st C# program

I am just starting out learning C# as my first programming language, I started learning about a week ago. This is my first program I have written. It will take user input to convert temperature values. Let me know what you guys think and any suggestions/tips are appreciated!

Here is an example of what the program outputs when ran:

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Enter a value to be converted

25

Please specify if your value inputed is Celcius with a 'c', Fahrenheit with a 'f' and Kelvin with a 'k'

c

25 Celsius is equal to 298.15 Kelvin.

25 Celcius is equal to 77 Fahrenheit.

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​

using System;

namespace Learning_2
{
    class MainClass
    {
        public static void Main(string[] args)
        {
            Console.WriteLine("Enter a value to be converted");
            int numValue = Convert.ToInt32(Console.ReadLine());

            Console.WriteLine("Please specify if your value inputed is Celcius with a 'c', Fahrenhite with a 'f' and Kelvin with a 'k'");
            string temperatureScale = Console.ReadLine().ToLower();


            //convert Celcius to Kelvin and Farhenheit
            if (temperatureScale.Equals("c"))
            {
                Console.WriteLine("{0} Celsius is equal to {1} Kelvin. \n{0} Celsius is equal to {2} Fahrenheit.", numValue, Celsius_Kelvin(ref numValue, ref temperatureScale), Farhenheit_Celsius(ref numValue, ref temperatureScale));
            }

            // Convert Kelven to Celsius and Farhenheit
            if (temperatureScale.Equals("k"))
            {
                Console.WriteLine("{0} Kelvin is equal to {1} Celsius. \n{0} Kelvin is equal to {2} Fahrenheit.", numValue, Celsius_Kelvin(ref numValue, ref temperatureScale), Farhenheit_Kelvin(ref numValue, ref temperatureScale));
            }
            //Convert Fahrenheit to Celsius and Kelvin
            if (temperatureScale.Equals("f"))
            {
                Console.WriteLine("{0} Fahrenheit is equal to {1} Celsius. \n{0} Fahrenheit         is equal to {2} Kelvin.", numValue, Farhenheit_Celsius(ref numValue, ref temperatureScale), Farhenheit_Kelvin(ref numValue, ref temperatureScale));
            }
        }
        // Methods
        // Convert Celsius and Kelvin back and fourth
        static ValueType Celsius_Kelvin(ref int numValue, ref string temperatureScale)
        {
            if (temperatureScale.Equals("c"))           //Celsius to Kelvin
            {
                double celsiusToKelvin = numValue + 273.15;
                return celsiusToKelvin;
            }

            if (temperatureScale.Equals("k"))           //Kelvin to Celsius
            {
                double kelvinToCelsius = numValue - 273.15;
                return kelvinToCelsius;
            }
            return null;
            }

            //Convert Farhenheit and Celsius back and fourth
            static ValueType Farhenheit_Celsius(ref int numValue, ref string temperatureScale)
            {
                if (temperatureScale.Equals("c"))       //Celsius to Fahrenheit
                {
                    double celsiusToFarhenheit = (numValue * 9 / 5) + 32;
                    return celsiusToFarhenheit;
                }

                if (temperatureScale.Equals("f"))       //Fahrenheit to Celsius
                {
                    double celsiusToFarhenheit = (numValue - 32) * 5 / 9;
                    return celsiusToFarhenheit;
                }
                return null;
            }

            //Convert Kelvin and Fahrenheit back and fourth
            static ValueType Farhenheit_Kelvin(ref int numValue, ref string temperatureScale)
            {
                if (temperatureScale.Equals("f"))       //Fahrenheit to Kelvin
                {
                    int farhenheitToKelvin = (numValue * 9 / 5) + 32;
                    return farhenheitToKelvin;
                }

                if (temperatureScale.Equals("k"))       //Kelvin Fahrenheit
                {
                    double kelvinToFarhenheit = (numValue - 273.15) * 9 / 5 + 32;
                    return kelvinToFarhenheit;
                }
                return null;
            }
        }
    } 

​