Calling R workbook in Databricks

Let's say I create a basic function in R:

Addn <- function(X,n)
  {
  X + n
  }

and this is saved to a Databricks workbook; some filepath: "/shared/x/y/z/Addnfunction"

In RStudio, I would typically call that function from another script by writing something like:

source("/shared/x/y/z/Addnfuntion.r")

If I open a new databricks notebook and want to call the above function (example, a shared team function) and use the "source" methodology I just get an error in regards to the function/connection.

Is there a best practice for leverage shared functions/scripts in R for databricks?