9 Use the graph below to answer the following questions: P 20 Price (dollars) 12 10 Demand Quantity a. The elasticity of demand at a price of $12 is b . The elasticity of demand at a price of $4 is C. At point A, if price increases by a small amount, total revenue (rises, falls, remains constant), and marginal revenue is positive, negative, zero). d. At point B. if price decreases by a small amount, total revenue (rises, falls, remains constant), and marginal revenue is (positive, negative, zero)