Open the Grade Solution (Grade Solution.sln) file contained in the ClearlyVB2012 Chap17Grade Solution folder. The application should display a letter grade, which is based on the average of three test scores. If the average is at least 90, the grade is A. If the average is at least 80 but less than 90, the grade is B. If the average is at least 70 but less than 80, the grade is C. If the average is at least 60 but less than 70, the grade is D. If the average is below 60, the grade is F. Code the application, using a function to return the appropriate letter grade. Save the solution and then start and test the application. Close the Code Editor window and then close the solution.