Need to use:

Windows Forms App (NET Framework) Visual C# Exercise 5-4 m named GradeTopDown that lets you to do the following Create a Tater a score (0-100) into a TextBox named txtScore, and compute the letter grade by clicking a button. 90, 80, 70 for A, B and C, respectively. The structure chart of the task to process the grade is as follows: Process Grade Score ScoreGrade Score, Grade Get Valid Score Grade Display Score & Grade The Click event handler of the button must call three separate methods, corresponding to the three subtasks, described below: A method named Get ValidScore that gets the name and score from the TextBoxes, validates the score and passes them to the Click event handler. A second method named Grade that computes the letter grade. Pass the score from the calling program to Grade. The method must return the letter grade without using a parameter. (This method is the same as in Exercise 5-3.) I. 2. A third method that displays the name and letter grade. Pass the name and letter grade as parameters to this method