The cost c (in dollars) per unit of making x photocopies at the office shop is given below.

--18 cents for at most 20 copies
--12 cents for more than 20 copies up to 50
--9 cents for more than 50 copies but less than 100
--5 cents for 100 copies or more but up to 200
--3 cents for more than 200 copies

(a) write the piecewise-defined function that represents the situation.
(b) explain why it would not be cost-effective to make 150 photocopies.