This exercise is reasonably straightforward. You answers should look something like this.
Add item to shopping cart
Remove item from shopping cart
Show running total for cart
Tasks for Story 1: Add Item to Shopping Cart
Test for adding normal item to cart
Test for adding null item to cart
Test for adding non existent item to cart
Code to make tests run
User interface to add items
Connect user interface to code
Check into source control and integrate with rest of system
Tasks for Story 2: Remove Item from Shopping Cart
Test for removing item from ...