The average speed of a train is 180% of the average speed of a car. The car covers a distance of 990 km in 15 hours. The time taken (in hours) by the train to cover the distance of 891 km is:
1
9\(\frac{1}{2}\)
2
7\(\frac{1}{2}\)
3
6\(\frac{1}{2}\)
4
5\(\frac{1}{2}\)