MICROECONOMICS: Optimal quantity produced in a Perfect Competition Market Suppose the Total Cost function of a firm in Perfect Competition is
  given by: $$C(q) = 450 + 15q + 2q^2$$
  
  The market price is $P = 15$ per unit
  
  Determine the optimal quantity produced by the firm


The trouble I'm having with this is a friend suggests the optimal quantity is q = 25 but that doesn't make sense to me.

Because when we calculate Marginal Cost = Marginal Revenue we get:

$$4q + 15 = 15$$

Which will yield an optimal quantity of 0 and not 25 when we solve for q.

The only way I can see it being equal to 25 is if the price is 115 and not 15 because of some typo. Any thoughts?
A typo seems very probable; more importantly, your procedure and concepts of setting MC=MR to solve for profit maximisation is definitely correct, regardless of the numbers being plug into the question.