cost of road service. rick's automotive charges $50. plus $15. for each (15min) unit of time when making a road call. twin city repair charges $70. plus $10. for each unit of time under circumstances would it be made economical for a motorist to call rick's.

Solution:

      Let the no. of hours = x

      50 + 15x < 70 + 10x

    15x - 10x < 70 - 50

               5x  < 20

                 x < 20/5 = 4

                 x < 4