Alandscaping company charges $100 plus $15 per hour. another company charges $75 plus $17 per hour. how long is a job that costs the same no matter which company is used?

Let h = number of hours

100 + 15h = 75 + 17h        solve for h
          100 = 75 + 2h          subtract 15h from both sides
             25 = 2h                 subtract 75 from both sides
          12.5 = h                   divide both sides by two

You would have to work 12 hours and 30 minutes for both companies to cost the same.