The demand, Q, for a certain good depends on its own price, P, and the price of an alternative good, PA, according to Q = 30 − 3P + PA
(a) Find Q if P = 4 and PA = 5.
(b) Is the alternative good substitutable or complementary? Give a reason for your answer.
(c) Determine the value of P if Q = 23 and P_A = 11.