The consumer surplus is 11.25.
Consumer surplus is the difference between the willingness to pay of a consumer and the price of the good.
Consumer surplus = willingness to pay – price of the good
The consumer surplus on a graph can be determined by calculating the area of a triangle.
Area of a triangle = 1/2 x base x height
1/2 x 5 x (9 - 4.5) = 11.25
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