Im not sure if I understand, you mean just this?
Code:
Private Function GetMiltiply(pNumber1 As Double, pNumber2 As Double) As String
    GetMiltiply = Format(pNumber1 * pNumber2, 0)
End Function
Code:
MsgBox GetMiltiply(1.23456789123457E+107, 9.87654321987654E+107)