20.50 * 0.8 = $16.40
16.40 * 0.4 = $6.56
Final selling price = $6.56
Answer:
4 times 3 is 12 and 12-17 is -5.
Step-by-step explanation:

You are taking two times a number, which is defined as x. That is equivalent to 2x. Then, you are adding three more to that product.
(150 miles/week) x (1 gallon / 25 miles) x (3 $/gallon)
= (150 x 1 x 3) / (25) (miles-gallon-$ / week-miles-gallon)
= 18 $/week .