The given situation is shown in the following figure
Velocity of river, vr=3ms−1 Velocity of boat, vb=15ms−1 Width of river =AB=200m According to question, we have to calculate distance BC. Time taken by boat to cross the river, t=‌
AB
vb
=‌
200
15
=‌
40
3
s Since, boat covers horizontal distance BC due to it own velocity. Hence, ‌‌BC=vr×t=3×‌