The extra amount that Mary would pay for apples under a monopoly instead of perfect competition is B. $3
Calculations and Parameters:
From the complete information,
There are images of the prices that can be gotten under a monopoly and the ones that can be gotten in a perfect competition by Mary.
The marginal cost which is graphed against the pound of apples and the price shows Mary would pay $15 and the marginal revenue shows that Mary would pay $12.
Hence, the difference between them, which is the extra amount to be paid would be $15-$12
=$3
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