To use an InputBox and store the input you must keep in mind that the InputBox will always return a String value. So you will need to convert the String into the appropriate data type and store that value in your Numeric variable.
I didn't include a Try/Catch around the actual conversion, but I would highly recommend that you do just that. This is to avoid any issues if the user should enter a character other than a number.
Another important note, ALL Functions return a value and typically are called in the same manner, so that the value returned is stored directly into a variable or used in some type of output, like a MessageBox.
Example:
CODE
Dim myVar As String
Dim myNum As Double
myVar = InputBox("Enter a number")
myNum = CDbl(myVar)
Does this answer your question?