Class Product
  Protected Price As Double
  Protected Shipping As Double

  Public Overridable Function CalculatePrice() As Double
    CalculatePrice = Price + Shipping
  End Function
End Class

Class LargeProduct
  Inherits Product

  Protected ShippingSurcharge As Double

  Public Overrides Function CalculatePrice() As Double
    CalculatePrice = MyBase.CalculatePrice() + ShippingSurcharge
  End Function
End Class