If the input box was for example A3 then this should work
Range("A5").Value = Range("A3").Value * 0.15
Save as a macro then assign the macro to the button
Is this what you mean ?...
Or, would it not be easier to just assign a formula to cell A5
=a3*0.15
as soon as you tabbed off, the value gets updated, no pressing of buttons required.
(hhmm, thought about this a little more).
Of course the other way is to create an input box that appears, enter the number and the result displayed and to do that your macro code would look like...
Sub NumericDataType()
Dim lNum As Long
On Error Resume Next
Application.DisplayAlerts = False
lNum = Application.InputBox _
(Prompt:="Please enter a number", _
Title:="Enter a Number", Type:=1)
On Error GoTo 0
Application.DisplayAlerts = True
lNum = lNum * 0.15
Range("A5").Value = lNum
End Sub