The answer is c.
The discount is 20% off, right? What's 20% of 35? To do that, you need to do the problem 35*.20, because .20 is equivalent to 20%. Remember how it is 20% off? That means subtract here. When you do 35*.20, you'll get 7. Now, subtract 7 from 35. 35-7=28, and your answer is in money; $28.00. :)