This really isn't that difficult. I sure hope you're just starting out and actually in a class doing this.
You need to think through the problem logically. What do you need to do to solve it?
Well, you need to go through each item in the ListView and sum up their values.
Then, divide that value by the total number of items, right? What exactly are you unclear about?
Dim sum as Long = 0
For Each lvItem as ListViewItem in ListView1.Items
sum += CInt(item.SubItems(0).Text)
Next
Label1.Text = sum / ListView1.Items.Count
If you can't understand something as simple as that, maybe this isn't the profession for you.