Ok I'm trying to learn python and I have come across a problem I need to solve for the exercise I'm doing in teachig yourself python in 24 hours lesson 2

I' supposed to wwrite a single line of code that solves this problem: I'm buying office supplies the total is 10 dollars but I have a 30% percent discount and I need to add 5% sales tax and 7.85 for shipping

This is how I'm thinking it should go:

10 - 10 * .30 (thats going to give me the price after discount which is 7 dollars) so I should then take that formula and add on the sales tax:

10 - 10 * .30 + 10 - 10 * .30 * .05 (the problem is I wind up with 16.85 which isnt right because the whole problem should equal $15.20)

So anybody have a clue where I'm going wrong