Calculate the equilibrium price and quantity.

Step 1: Calculate the equilibrium price and quantity.
The given equations are:
Demand: $Q_D = 1200 - 2P$
Supply: $P = 150 + Q_S \implies Q_S = P - 150$

At equilibrium, quantity demanded equals quantity supplied ($Q_D = Q_S$).

$$1200 - 2P = P - 150$$ $$1200 + 150 = P + 2P$$ $$1350 = 3P$$ $$P_E = \frac{1350}{3}$$ $$P_E = 450$$

Substitute $P_E =