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

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.