A car averages 75 mph for the first 4 hours of a trip and averages 60 mph for each additional hour. The average speed for the entire trip was 70 mph. How many hours long is the trip? Choose the correct choice from the following:	A) 6	B) 78	C) 8	D) 9	E) 10

Rationale: "let the time for which car averages 60 mph = t 70 * ( t + 4 ) = 75 * 4 + 60 t = > 10 t = 20 = > t = 2 total duration of the trip = 4 + 2 = 6 answer a"
Answer: A