Please see my attached work.

I have indicated what my wrong answer was and what the correct answer is. I do not see where I made a mistake.

Problem:

Suppose the demand for a certain brand of a product is given by D(p)= p^2/216 + 500, where p is the price in dollars.

If the price, in terms of the cost c, is expressed as p(c)= 3c9,

find the demand function in terms of the cost.

11. Same. D = - P 2 216 -+ 500 =) D = - ( 30-9)2 + 500 C = 3 0 - 9 241 6 - - 32 ( C-9) - +500 - - 9 (c2-18c+811) + 500 21b 216 ( C - 9 ) (( - 9 ) = - (C2- 18c+ 81 + 500 wrong 1 = (2- 96- 96+81 24 =(2 - 18 6+ 81 Correct + 500 answer 24