
Profit maximization
Been on this problem for over an hour please help,
I keep getting my derivative at .12x^210.8x1200
with zeros at 154.659, 64.659 I dont know if thats right though
here is the question:
If C(x) = 13000 + 400x  0.6x2 + 0.004x3 is the cost function and p(x) = 1600  6x is the demand function, find the production level that will maximize profit. (Hint: If the profit is maximized, then the marginal revenue equals the marginal cost.)

P(x)=Revenue function  cost funtion
Take the derivative and set equal 0

I did that but I get .12x^210.8x1200=0 which doesnt do anything for me

What is your revenue function?