Question

A plumber chargers $50 for a service call plus $75 per hour. The total of these costs (in dollars) is a function C(t) of the time t (in hours) on the job. For how many hours will the cost be $200? $300? Explain answer.

Answer 1

Cost=50+70*(t)

200=50+70*(t)
150=70*(t)
t=2.14 Hours

300=50+70*(t)
250=70*(t)
t=3.57 Hours

Answer 2

So cost=50+75t
so 200=50+75t
subtract 50 from both sides
150=75t
divide both sides by 75
2=t
$200=2 hours

50+75t=cost
300=50+75t
subtract 50 from both sides
250=75t
divide both sides by 75
10/3=t=200 mins=3hours 20 mins=$300