Public Class Form1

    Private Sub TextBox1_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles TextBox1.TextChanged
        Dim letterGrade As String
        Dim percentScore As Integer
        letterGrade = TextBox1.Text
        Select Case letterGrade
            Case "F"
                percentScore = 0
            Case "D"
                percentScore = 45
            Case "D+"
                percentScore = 50
            Case "C-"
                percentScore = 55
            Case "C"
                percentScore = 60
            Case "C+"
                percentScore = 65
            Case "B-"
                percentScore = 70
            Case "B"
                percentScore = 75
            Case "B+"
                percentScore = 80
            Case "A-"
                percentScore = 85
            Case "A"
                percentScore = 90
            Case Else
                percentScore = 0
                TextBox1.Text = ""
        End Select
        TrackBar1.Value = percentScore
        Label2.Text = "Percentage score: " & CStr(TrackBar1.Value) & " %"
    End Sub

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        TrackBar1.Value = 0
    End Sub

    Private Sub TrackBar1_Scroll(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles TrackBar1.Scroll
        Dim letterGrade As String
        Dim percentScore As Integer
        percentScore = TrackBar1.Value
        If percentScore < 45 Then 'score < 45
            letterGrade = "F"
            'score >= 45
        ElseIf percentScore < 50 Then '45 <= score < 50
            letterGrade = "D"
        ElseIf percentScore < 55 Then '50 <= score < 55
            letterGrade = "D+"
        ElseIf percentScore < 60 Then
            letterGrade = "C-"
        ElseIf percentScore < 65 Then
            letterGrade = "C"
        ElseIf percentScore < 70 Then
            letterGrade = "C+"
        ElseIf percentScore < 75 Then
            letterGrade = "B-"
        ElseIf percentScore < 80 Then
            letterGrade = "B"
        ElseIf percentScore < 85 Then
            letterGrade = "B+"
        ElseIf percentScore < 90 Then '85 <= score < 90
            letterGrade = "A-"
        Else ' scor >= 90
            letterGrade = "A"
        End If
        TextBox1.Text = letterGrade
        TrackBar1.Value = percentScore
        Label2.Text = "Percentage score: " & CStr(TrackBar1.Value) & " %"
    End Sub
End Class