Newbie Model Question

I'm building a shop in rails as a learning excercise. I've got to the
last part when I'm sending out e-mail order confirmations. The e-mails
contain a list of each line item the customer ordered, I also want to
display the catgory name the customer ordered from.

The database is setup: Category > Product > Line_item.
So I want to navigate back from line_item > product > category so i
can display the category name in the email however im not sure how I
tell it to find the category name from the item.

Be greatful for anyhelp.

Assuming all the associations are setup correctly.

You can also set it up using :through so that you can just to