Answer:
3 km per hour
Step-by-step explanation:
You can deduct the answer instinctively since both the distance and the time of the descent are expressed in /5... so you can just get rid of the '/5' in both instances to get the result: 3 kilometers in 1 hour.
But you can also find it easily using the cross-multiplication system:
Then you multiply each side by 5 to get
3 km = 1 hour
Thus the rate of descent is of 3 km per hour.