the problem deals with applications of derivatives. the problem is: until recently hamburgers at the city sports arena costs $4 each the food concessionaire sold an average of 10,000 hamburgers on a game night. when the price was raised to $4.40, hamburger sales dropped off to an average of 8000 per night.

a) find the price of a hamburger that will maximize the nightly hamburger revenue.

I know that in order to do that, we have to use the point slope formula to find the demand function. I got p-4=[(4-4.4)/(10,000-8000)] [(x-10000).

I don't get why the answer key has p-2=[(2-2.4)/(10,000-8000)] [(x-10000) and still got the correct answer?