I need explanation

16.6 (0) Schrecklich and LaMerde are two justifiably obscure nineteenth- century impressionist painters. The world's total stock of paintings by Schrecklich is 100, and the world's stock of paintings by LaMerde is 150. The two painters are regarded by connoisseurs as being very similar in style. Therefore the demand for either painter's work depends both on its own price and the price of the other painter's work. The demand function for Schrecklichs is Ds(P) = 200-4PS -2PL, and the demand function for LaMerdes is DL(P) = 200 -3PL - Ps, where Ps and PL are respectively the price in dollars of a Schrecklich painting and a LaMerde painting. (a) Write down two simultaneous equations that state the equilibrium condition that the demand for each painter's work equals supply. The equations are 200 -4Ps -2PL = 100 and 200 - 3PL - PS = 150. (b) Solving these two equations, one finds that the equilibrium price of Schrecklichs is 20 and the equilibrium price of LaMerdes is 10