Write code that will be used by a Shopping cart service to enforce rules on the order
eg.
Offer free 2 day shipping on orders > $35 if customer is not a prime member
Offer free 2 day shipping on all orders if customer is a prime member
Offer free 1 day shipping for order that are > $125
Offer free 2 hour shipping for prime customer that have > $25 and the items are grocery items
Make this extensible to add other rules in the future
Apply a 10% discount if an item has been marked for subscribe and save