Assuming you have created a textbox to accept a number, you need to just multiply that number by 0.035.
Somthing like this would do it.
Public Class Form1
Private Sub TextBox1_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles TextBox1.TextChanged
End Sub
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim percentage As Double
percentage = CDbl(TextBox1.Text)
percentage = percentage * 0.035
Label1.Text = percentage
End Sub
Private Sub Label1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Label1.Click
End Sub
End Class