Jake hires a septic system contractor to dig trenches for his new septic tank. The cost to hire the contractor is a fixed cost of $160 plus an additional $70 per hour. Which expression below describes the average cost of an x-hour job?
A. 160x+70/x dollars per hour
B. x/70x+160 dollars per hour
C. 70x+160/x dollars per hour
D. 160+70/x dollars per hour