Please help me with this story problem

Question

At a school-sponsores car wash, the fees charged were: $5 per car,$8 per pickup truck, $10 per full-size van. Twice as many cars were washed as pickup trucks. The amount collected for washing cars and pickup trucks was $360. A total of $410 was collected at the car wash. Find the number of cars washed.

Answer 1

Alright, tough one.

c = 2p

5c + 8p = 360

Suuuuubstitute!

5(2p) + 8p = 360

10p + 8p = 360

18p = 360

p = 20

c = 2(20)

c = 40 cars