Try this...
  Dim a, b As String
  a = TextBox1.Text
  b = (TextBox2.Text)
  Dim discount as Double
  Select Case a
    Case "Julius B. Tanguilig":
      discount = 09268862690 / 425673
      TextBox2.Text = Convert.ToString(discount)
    Case "Jodel D. Avendano":
      discount = 09053146571 / 432467
      TextBox2.Text = Convert.ToString(discount)
    Case "Mara Grantoza":
      discount = 09357648907 / 423094
      TextBox2.Text = Convert.ToString(discount)
    Case Else:
      TextBox2.Text = String.Empty
  End Select