The Following Sample of Code Contains Errors

The following sample of code contains errors. Rewrite the incorrect statements to correct all errors.
-Structure ExamGrades
Public decExam1 As Decimal
Public decExam2 As Decimal
Public decExam3 As Decimal
End Structure
---------------------------
Private Function CalcAverage(ByVal grades As Decimal)As Decimal
' calculates and returns the average grade
Dim decSum As Decimal
decSum = grades.Exam1 + grades.Exam2 +
grades.Exam3
Return decSum * 3
End Function
---------------------------
Private Sub btnAverage_Click(ByVal sender As Object,ByVal e As System.EventArgs)Handles btnAverage.Click
' display the average exam grade
Dim threeGrades As ExamGrades
Dim decAverage As Decimal
Decimal.TryParse(txtGrade1.Text,decExam1)
Decimal.TryParse(txtGrade2.Text,decExam2)
Decimal.TryParse(txtGrade3.Text,decExam3)
decAverage = CalcAverage(threeGrades)
lblResult.Text = decAverage.ToString("N1")
End Sub