Sub Mart Inc. needs to decide the optimal price to charge and the optimal quantity to supply in the market. The demand function of the product is given as QD=40-2P, while the supply function of the product is given as QS=2P where P is the price, QD is quantity demanded, and QS is quantity supplied. Solve the following demand function is given as: QD=40-2P. Calculate the equilibrium price and quantity. (5Marks)

Q3.Consider the demand for apples. If the prices of a substitute good(bananas) increases and the price of a complement good (apple pie) increases, can you tell for sure what will happen to the demand for apples? Why or why not? Illustrate your answer with a graph.