Tax only applied to hard copy not to electronic copy of a book

[cheloricardo]

Thanks for reading this

The user see the description of the product and then chooses between two attributes (radio buttom)
The product (a book) that's taxable, now it has as attributes
a) hard copy
b) electronic copy.

What do I need to do so when they choose electronic copy don't charge the
tax associated with the product?

Because we are not sending the product they are downloading it