Answer: John swam 18060 meters for those 3 weeks.
Explanation:
1 kilometer = 1000 meters
0.86km = 0.86*1000 = 860m
Using the information above, we can see that John swam 860 meters each day.
1 week = 7 days
3 weeks = 3*7 = 21
21*860 = 18060 m
Therefore, John swam 18060 meters in those three weeks.