Where am I going wrong - Maximizes the profit

[Happy101]

I'm trying to figure out the maximum profit and plot the points on the x. Here's the information I have:
--------------------------
Product production cost (C)
Production quantity (q)
Profit (P)
Product price is 1500.

C(q) = (1/6)q^3 - 30q^2 + 2,500q
q ≥ 0
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Here's what what I'm doing but I'm doing something wrong... what is it?

Profit (P) = Sales revenue (R) - Production cost (C) = (Price × Production quantity) - (C(q)) = (1,500 × q) - (1/6)q^3 - 30q^2 + 2,500q

(1/6)q^3 - 30q^2 + 1,000q
-1/2q^2 - 60q + 1,000 = 0
So 60 should be the highest and x=20 and x=100

The above doesn't seem to be correct. Any help to know where I'm going wrong would be very much appreciated

 

[blamocur]

= (1,500 × q) - (1/6)q^3 - 30q^2 + 2,500q

Check your signs here.

 

[Happy101]

Do you mean it should be:
(1500 × q) - ( (1/6)q^3 - 30q^2 + 2500q)
-(1/6)q^3 + 30q^2 - 1,000q

 

[blamocur]

Do you mean it should be:
(1500 × q) - ( (1/6)q^3 - 30q^2 + 2500q)
-(1/6)q^3 + 30q^2 - 1,000q

Are you missing a "=" sign here?