In this exercise, you modify the Grade Calculator application from this chapter’s Apply lesson. Use Windows to make a copy of the Grade Solution folder. Rename the copy Grade Solution-Intermediate. Open the Grade Solution.sln file contained in the Grade Solution-Intermediate folder.
a. Open the CourseGrade.vb file. The DetermineGrade method should accept an integer that represents the total number of points that can be earned in the course. (Currently, the total number of points is 200: 100 points per test.) For an A grade, the student must earn at least 90% of the total points. For a B, C, and D grade, the student must earn at least 80%, 70%, and 60%, respectively. If the student earns less than 60% of the total points, the grade is F. Make the appropriate modifications to the DetermineGrade method and then save the solution. 

b. Unlock the controls on the form. Add a label control and a text box to the form. Change the label control’s Text property to “&Maximum points:” (without the quotation marks). Change the text box’s name to txtMax. Lock the controls and then reset the tab order. 

c. Open the form’s Code Editor window. The txtMax control should accept only numbers and the Backspace key. Code the appropriate procedure. 

d. The grade should be cleared when the user makes a change to the contents of the txtMax control. Code the appropriate procedure. 

e. Modify the frmMain_Load procedure so that each list box displays numbers from 0 through 200. 

f. Locate the btnDisplay_Click procedure. If the txtMax control does not contain a value, display an appropriate message. The maximum number allowed in the txtMax control should be 400; if the control contains a number that is more than 400, display an appropriate message. The statement that calculates the grade should pass the maximum number of points to the studentGrade object’s DetermineGrade method. Make the necessary modifications to the procedure.
g. Save the solution and then start and test the application.