Detailed Instructions: The task is to generate the correct answer for a given math problem.
Q: Problem: a train travels at the rate of 10 miles / hr for the first hour of a trip , at 20 miles / hr for the second hour , at 30 miles / hr for the third hour and so on . how many hours will it take the train to complete a 360 - mile journey ? assume that the train makes no intermediate stops .
A:
8