The Total Cost (C) and the Total Revenue (R), in dollars, for the production and

The Total Cost (C) and the Total Revenue (R), in dollars, for the production and sale of q hair dryers are given by:
C(q) = 2000 + 5q     and      R(q) = 40q – 0.05q2
Find the interval(s) of quantity q on which the Profit (P) is (i) increasing and (ii) decreasing.