ListBoxes in Visual Basic - vb.net

Question

I have an assignment where the user will enter numbers into a list box. When the user is done entering numbers, it will compute the average and the standard deviation.(Our professor does not want us to use built in standard deviation functions) The program will have a context menu and these are the guidelines for creating the menu: You must create a subroutine called SetMenu. It is used to enable and disable context menu based on the contents of the list. When the list is empty,Clear is disabled. When the list has at least one number in it,Clear is enabled. When nothing is selected, Delete Item is disabled. When something is selected, Delete Item is enabled.
That is where I need help, creating that subroutine.
Here is my code:
Option Strict On
Public Class Form1
Private Sub AddBtn_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles AddBtn.Click
ListBox.Items.Add(InputBox.Text)
InputBox.Text = ""
End Sub
Private Sub ComputeBtn_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ComputeBtn.Click
Dim sum, x, number, numberSum, subtractedNum As Integer
Dim average, insideRoot, squaredRoot As Double
For x = 0 To ListBox.Items.Count - 1
ListBox.SelectedIndex = x
number = Integer.Parse(ListBox.SelectedItem.ToString)
sum = sum + number
average = sum / ListBox.Items.Count
Next
AverageLbl.Text = average.ToString
For x = 0 To ListBox.Items.Count - 1
ListBox.SelectedIndex = x
number = Integer.Parse(ListBox.SelectedItem.ToString)
subtractedNum = CInt((number - average) ^ 2)
numberSum = numberSum + subtractedNum
insideRoot = (numberSum / (ListBox.Items.Count - 1))
squaredRoot = insideRoot ^ (1 / 2)
Next
DeviationLbl.Text = squaredRoot.ToString("N2")
End Sub
Private Sub ClearMenu_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ClearMenu.Click
ClearMenu.Enabled = False
SetMenu()
ListBox.Items.Clear()
End Sub
Private Sub DeleteMenu_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles DeleteMenu.Click
ListBox.Items.Remove(ListBox.SelectedItem)
End Sub
Private Sub InputBox_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles InputBox.TextChanged
If IsNumeric(InputBox.Text) And InputBox.Text <> "" Then
AddBtn.Enabled = True
Else
AddBtn.Enabled = False
End If
End Sub
Private Sub SetMenu()
'Need help here
End Sub
End Class

Answer 1

How about:
Private Sub toggleContextMenuItems()
ClearToolStripMenuItem.Visible = (ListBox1.Items.Count > 0)
DeleteToolStripMenuItem.Visible = (ListBox1.SelectedIndex > -1)
End Sub
Then call this method when needed.