New to outputting in VB for Object Oriented Programming

I believe I have the correct calculation for obtaining a persons age if they put in their birth date and maybe even correct for the GPA calculation based off of three course grades entered as Integers and returned as a GPA double, but do not understand how to output this all in Listbox from one button click using two classes and inheritance. SMH

Public Class Form1

    Dim dateofBirth As Date
    Public Class Person
        Public first As String
        Public last As String
        Public dateofBirth As Date
        Function Age() As Integer
            Dim today As Date = Now()
            Dim years As Integer = today.Year - dateofBirth.Year
            Return years
        End Function
    End Class

    Public Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click



        ListBox1.Items.Add("Name: " & first.Text & " " & last.Text)
        ListBox1.Items.Add("")
        ListBox1.Items.Add("Age: " & (birth.Age))

    End Sub

    Public Class Student
        Inherits Person
        Dim eGrade As Double
        Dim mGrade As Double
        Dim sGrade As Double






        Public Function EnglishGPA() As Double
            Dim GPA(0) As Double
            If CInt(eGrade) >= 90 Then
                GPA(0) = 4
            ElseIf CInt(eGrade) >= 80 Then
                GPA(0) = 3
            ElseIf CInt(eGrade) >= 70 Then
                GPA(0) = 2
            ElseIf CInt(eGrade) >= 60 Then
                GPA(0) = 1
            ElseIf CInt(eGrade) < 60 Then
                GPA(0) = 0
            End If

            Return GPA(0)
        End Function


        Public Function MathGPA() As Double
            Dim GPA(1) As Double

            If CInt(mGrade) >= 90 Then
                GPA(1) = 4
            ElseIf CInt(mGrade) >= 80 Then
                GPA(1) = 3
            ElseIf CInt(mGrade) >= 70 Then
                GPA(1) = 2
            ElseIf CInt(mGrade) >= 60 Then
                GPA(1) = 1
            ElseIf CInt(mGrade) < 60 Then
                GPA(1) = 0
            End If

            Return GPA(1)


        End Function



        Public Function ScienceGPA() As Double
            Dim GPA(2) As Double

            If CInt(sGrade) >= 90 Then
                GPA(2) = 4
            ElseIf CInt(sGrade) >= 80 Then
                GPA(2) = 3
            ElseIf CInt(sGrade) >= 70 Then
                GPA(2) = 2
            ElseIf CInt(sGrade) >= 60 Then
                GPA(2) = 1
            ElseIf CInt(sGrade) < 60 Then
                GPA(2) = 0
            End If

            Return GPA(2)

        End Function


        Public Function TermGPA() As Double

            Dim TGPA As Double
            TGPA = (EnglishGPA() + MathGPA() + ScienceGPA() / 3)


            Return TGPA
        End Function

    End Class
End Class