The demand and supply lines in a market are as follows:
Demand: P = 21 - 2Q
Supply: P = 3+Q ,
where P is the price in dollars (vertical axis) and Q is the quantity in pounds (horizontal axis).
(a) Give a graph and solve for equilibrium price and quantity.
(b) Now suppose a tax is imposed so that the price paid by the demander is $13 and the price received by the supplier is $7. Calculate the tax revenue.