A) Means that you will get 144.75 off, so no, not that. How I got my answer there is taking 579 and multiplying it by .25. That means the price of the computer while using coupon A is $434.25.
B) Is $150 dollars off, so simply the price is $429, cheaper than a.
C) Do 5% of 579, which is 28.95, so add that to 75, which means you'll get 103.95 dollars off of that computer. Which makes the computer 475.05 dollars. This is NOT the correct answer.
B) 10% of 579 is 57.9, and add 50 to that, which makes 107.9. Subtract 107.9 from 579 to get 471.1.
The cheapest computer (with coupon) is B.
Hope I helped!