Producer surplus is the difference between the revenue a producer earns from selling a product and the minimum amount they are willing to accept for it. 

In a perfectly competitive market, producers are price takers. This means that a producer does not set their own price and sell the products at the prevailing market price. Consequently, the amount actually received by a firm is influenced by the market price of the product.

The firm's willingness to supply is determined by its supply curve. In the short run, the firm’s supply curve is represented by its marginal cost curve. The marginal cost indicates the additional cost incurred by producing one more unit of the product. 

To analyze the producer surplus, consider a firm that sells coffee machines in a perfectly competitive market. Since the market price is $150 per unit, the firm bases its supply decisions on its marginal cost of production.

Consider the marginal costs of producing each machine: $110 for the first unit, $120 for the second, $130 for the third, $140 for the fourth, and $150 for the fifth. The firm will continue producing coffee machines until the marginal cost equals the market price. In this case, the firm produces five units. Producer surplus is calculated as the sum of the difference between the market price and the marginal cost for each unit produced. Producer surplus for each unit is:

• 1st unit: $150 - $110 = $40
• 2nd unit: $150 - $120 = $30
• 3rd unit: $150 - $130 = $20
• 4th unit: $150 - $140 = $10
• 5th unit: $150 - $150 = $0 (no surplus)

Total producer surplus = $40 + $30 + $20 + $10 + $0 = $100

Thus, producer surplus shows how much producers gain by selling in a market.