We bought 85 hats at the store. Blue hats cost $6 and green hats cost $7. The total price was $540. How many green hats did we buy?  Choose the correct option
A) 36  B) 30  C) 40  D) 42  E) 44

Rationale: "let b be the number of blue hats and let g be the number of green hats . b + g = 85 . b = 85 - g . 6 b + 7 g = 540 . 6 ( 85 - g ) + 7 g = 540 . 510 - 6 g + 7 g = 540 . g = 540 - 510 = 30 . the answer is b ."
Answer: B