Car A leaves the airport at 9:00 am and travels at a constant rate of 30 km per hour. Car B leaves the airport at 9:30 am and travels in the same direction along the same highway at a constant rate of 34 km per hour. At what time will Car B be 12 km ahead of Car A? Choose one.
A) 3:45 pm	B) 4:00 pm	C) 4:15 pm	D) 4:30 pm	E) 4:45 pm
At 9:30 am, Car A will be 15 km ahead of Car B.   Car B travels at a rate 4 km per hour faster than Car A.   Car B needs to travel 27 km more than Car A in order to be 12 km ahead.   This will take 27 km/4 km per hour=6.75 hours.   Car B will be 12 km ahead at 4:15 pm.   The answer is 4:15 pm.
<result>C</result>
Car A leaves the airport at 9:00 am and travels at a constant rate of 30 km per hour. Car B leaves the airport at 9:30 am and travels in the same direction along the same highway at a constant rate of 34 km per hour. At what time will Car B be 12 km ahead of Car A?