Deleting node from linked list

Hi people. Nice to meet you. I'm trying to do the following assignment from Robert Sedgewick's book:

Quote

However, I have no idea how to implement this because I'm using references in a linked list not arrays.

I coded this:

package stack;

public class LinkedListStack<Item> {

    private Node first;
    private int N;


    private class Node 
    {
       Item item; 
       Node next;
    }
    
    public boolean isEmpty()
    { 
       return first == null; 
    }            
    
    public int size()
    { 
       return N;    
    }            
    
    public void delete(int k)
    {
        throw new UnsupportedOperationException();
    }            
    
    public void push(Item item)
    {
       Node oldfirst = first; 
       first = new Node();
       first.item = item; 
       first.next = oldfirst;
       N++;
    }
    
    public void peek()
    {
       System.out.println("Last node contains: " + first.item); 
    }        
    
    public Item pop()
    { 
       Item item = first.item;
       first = first.next;
       N--;
       return item;
    }            
}

package stack;

public class LinkedListStackTest {

    public static void main(String[] args) {
          
       LinkedListStack<String> lls = new LinkedListStack();  
       
       lls.push("a");
       lls.push("b");
       lls.push("c");
       lls.push("d");
       
       lls.peek();
    }
}