Cost and demand functions

[thatguy47]

For the given cost and demand function, find the production level that will maximize profit.

C(x) = 680 + 4x + 0.01x^2, p(x) = 12

The answer is 400 and whatever I do, I cant get that answer.

 

[tkhunny]

You need Revenue. Can you use Demand to create that?
You need Profit. Can you use Cost and Revenue to create that?