Microeconomics

Please help with these questions. I am getting them wrong... Please explain b) in more detail

(03.01-03.07 MQ) Auctio sells sprockets in a perfectly competitive market. Below are its short-run total variable costs at different output levels. The firm's fixed cost is $5. The market price of one sprocket is $8. Units | Total Variable Cost 0 $0 1 $12 2 $18 3 $22 4 $28 5 $35 6 $43 a. What is the average total cost of the 5th unit? b. What is the first unit of output where diminishing marginal returns have begun? c. What profit or loss would Auctio earn at its profit maximum? Show your work. d. Would Auctio operate in the short run? Explain. e. Would Auctio stay in the market in the long run? Explain