Explanation:
for an estimation just remember that
1 mile is a bit more than 1.5 km.
so, 15 miles × 1.5 = 15 + 15/2 = 15 + 7.5 = 22.5 km
therefore,
24.15 kilometers must be the correct answer.
FYI :
a quick check in the internet shows
1 mile = 1.60934... km
15 miles = 15 × 1.60934... = 24.1402... km
so, yes, 24.15 km is the correct answer option.