how to add fixed textbook cost as a line time to the invoice?

[Prostar]

I sell corporate training.

The cost for each class is set in its button. The cost for each class varies.

I also add an additional fixed charge of $25 for each textbook, detailed in the product description.

The customers enroll for one person for one class at a time.

How do I have the $25 textbook cost show as a line item when:

1. They select a class to buy, and,

2. Detailed as a line item on the invoice, and,

3. Totaled on the transaction.