Farmers living alone on an island both grow and consume corn. Their total benefit of 1 bushel of corn is $6, two is $11, three is $15, four is $18, and five is $20. Their total cost of growing one bushel is $1, two bushels is $3, three bushels is $6, four is $10, and five is $15. What are the marginal benefit, the marginal cost, and the change in net benefit of each bushel? How many bushels should the farmers grow to maximize net benefits?