Linked List Solutions CHP 5 Problem 1 pg65

I am extremely confused with how this book is written. For the first solution it says: “add the following function to your playground” :
private func printInReverse(_ node: Node?) {
// 1 guard let node = node else { return }
// 2 printInReverse(node.next)
}
I add it, then I follow the instructions and add the helper function:
func printInReverse(_ list: LinkedList) {
printInReverse(list.head) }
Where should this be added??? Where should prior function be added? - to Linked List file?? It says " from the original printInReverse Function" then it says add the following print statements. Please help “where are these added- as in what files??” Are there solutions somewhere?? I can see??

@ben_jammin You can find the solutions to all challenges in the last section of the book. I hope it helps!