coupon help on ps 4.53, need to add a item if otheres bought
My client sells training manuals and does classes with them. She wants me to configure the store so that if you by 100 of the manuals she will give you a free class. Her idea was a coupon code so she had some control with marketing. I was thinking that I could create a downloadable item (the class certificate) that would get added in to the cart when you
a) bought 100 copies of the book and
b) put in the coupon code.
She is also open to other ways to do this, but I need help in any case.