Suppose you were starting in the office cleaning service. We have spent $315 on equipment. To clean an office, you use four dollars worth of supplies. You charge $25 per office. How many officers must clean to break even?

Number of offices to be cleaned to cover the cost of equipment = 15

Cost of equipment = $.315 Cost of supplies = $.4 Charge per office = $.25

Number of offices to be cleaned to cover the cost of equipment = x

Then - 25x - 4x = 315

21x = 315

x=315

21=15

Number of offices to be cleaned to cover the cost of equipment = 15