Create a Windows Form with the following characteristics:

1. It should have
   1. An add button when clicked:
      1. checks if a checkbox is not set, then it would display "Hello World!" on the RichTextBox .
      2. if the check box is set, it adds "Hello World x!" to a RichTextBox. Where x starts at 0 and gets incremented on every "add" click. In an word if it is set it would display incremented "Hello world!"
   2. checkbox that can be set/unset
   3. a clear button that would clear the content of theTextRichBox
   4. An exit button that would end the run.

programming language is c#