Answer
a) Please see the picture.
b) Bert buys two bottles, and his consumer surplus is 4 dollars.
c) Bert buys three bottles, and his consumer surplus is 9 dollars.
Work Step by Step
a) The first image shows the demand schedule and the demand curve.
b) Bert would be willing to pay 7 dollars for his first bottle but pays only 4 dollars. Bert would be willing to pay 5 dollars for his second bottle but pays only 4 dollars. His surplus from the first bottle is 4 dollars (7-4), and his surplus from the second bottle is a dollar (5-4). This surplus is area $A$ on the second graph.
c) Bert would be willing to pay 7 dollars for his first bottle but pays only 2 dollars. Bert would be willing to pay 5 dollars for his second bottle but pays only 2 dollars. Bert would be willing to pay 3 dollars for his third bottle but pays only 2 dollars. His surplus from the three bottles is $(7-2)+(5-2)+(3-2)$, which is 9 dollars. The surplus is areas $A+B$ on the second graph.
