Walden Green provides custom farming services to owners of five-acre wheat fields. In July, he earned $2,400 by cutting, turning, and baling 3,000 bales. In the same month, he incurred the following costs: gas, $150; tractor maintenance, $115; and labor $600. His annual tractor depreciation is $1,500. What was Green's cost per bale? What was his revenue per bale? Should he increase the amount he charges for his services?