To calculate producer surplus, we must find the producer surplus on each pizza and add these surpluses together. For the 10,000th pizza, marginal cost equals $10 and producers receive $10, so the producer surplus on this pizza is zero. For the 5,000th pizza (highlighted in the figure), marginal cost is $6. So on this pizza, producer surplus is $10 minus $6, which is $4. For the first pizza, marginal cost is $2, so on this pizza, producer surplus is $10 minus $2, which is $8.

Producer surplus—the sum of the producer surpluses on the 10,000 pizzas that firms produce—is $40,000 a day, which is shown by the area of the blue triangle. The base of the triangle is 10,000 pizzas a day and its height is $8, so its area is