It took him 2.6 hours to reach the top
Data;
- Uphill = 6km
- Downhill = 4km
- Total time taken = 8 hours
<h3>Speed</h3>
Let us calculate the speed during uphill and downhill
Since the time it took them to descend is twice the time it took them to ascend,
- Let x represent the time taken to ascend

From the calculation above, it took him 2.6 hours to reach the top.
Learn more on speed here;
brainly.com/question/4931057
The solution to the problem is as follows:
Given: 2.5 lb
Asked: 2.5 lb -----> kg
Answer:
2.5 lb * ( 1 kg/2.2 lb) = 1.1 kg
Therefore, the weight of the book in kg is 1.1 kg.
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Here x=3
so, putting 3 instead of x