Progressive express left for New Delhi, increasing its speed in each hour. It started its journey from Lucknow, but after four each hour. It started its journey it met with accident. Its speed in the fourth hour was `(7)/(5)` times that of the third hour and the speed in the third hour was `(10)/(7)` times that of the second hour and in the second hour it was `(7)/(5)` times that of the first hour. If it would have been travelled with the half of the speed that f the third hour, then it would have gone 160 km less in the same time (i.e., in four hours). The average speed of the train during the journey of 4 hours was :

Options

A. 50 km/hr
B. 90 km/hr
C. 80 km/hr
D. can't be determined

Answer

B