The graph represents the demand for online subscriptions to Consumer Reports. A graph plots a demand curve with Quantity, millions of subscriptions to Consumer Reports online on the horizontal axis and Price of subscription on the vertical axis. The demand curve starts at 80 dollars on price and has a negative slope. The points marked on the curve as Quantity, millions of subscriptions to Consumer Reports online, and Price of subscription are 10, 40 dollars; 15, 20 dollars; and 20, 0 dollars. The efficient quantity of subscriptions is _____ million