Ronnie operates a lawn-care service. On each day, the cost of mowing the first lawn is $15, the cost of mowing the second lawn is $25, and the cost of mowing the third lawn is $40. His producer surplus on the first three lawns of the day is $100. If Ronnie charges all customers the same price for lawn mowing, that price is a. $20. b. $60. c. $80. d. $180.