Type mismatch Error VbSCript.

d dim obj1
	set obj1=CreateObject("Begineers.first")
   Dim lngReturnValue 
   Dim a
   a=5
    Dim b
	b=7
    obj1.AddNumbers a, b, lngReturnValue

    Wscript.Echo( "The value of a+b is: " & lngReturnValue)

    Set obj1 = Nothing

STDMETHODIMP Cfirst::AddNumbers(LONG Num1, LONG Num2, LONG* ReturnVal)
{
    // TODO: Add your implementation code here
 *ReturnVal = Num1 + Num2;
    return S_OK;
}