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