It is important to carefully go through all the information's that are given in the question. based on those given information's the answer to the question can be easily deduced.
Distance traveled by a person in 0.8 hours is = 20 km
Then
In 1 hour the distance traveled by the person = (20/0.8) * 1
= 20/0.8 km
= 200/8 km
= 25 km
So the distance traveled by the person in 1 hour is 25 km. I hope the procedure is clear enough for you to understand.