How do you use the LN function that is found on a Business Calculator in Visual Basic?

I need to know how call a function in Visual Basic that does the same thing as the LN button on a business calculator. I found the following on this site:

    Private Function Ln(ByVal Number As Double) As Double

        Ln = Log(Number) / Log(Exp(1))

    End Function

I get errors stating that the Log and Exp portions have not been declared. I thought that these were built-in function of VB?

My other part of my code calls this function as follows:

   'Now Call the function that performs the LN portion on a calculator
        Dim dblLN1, dblLN2 As Double

        dblLN1 = Ln(dblNumerator)
        dblLN2 = Ln(dblDenominator)

I am using Visual Studio 2008. Any help would be GREATLY appreciated.