Dhriti can swim 3 km/hr. in still water. If the velocity of the stream is 2 km/hr., find the distance travelled by her in upstream and downstream if the total time of travel is 12 hr.

Upstream speed = 3 - 2 = 1 km/h. Downstream speed = 3 + 2 = 5 km/h. Let upstream distance = downstream distance = d. Total time: d/1 + d/5 = 12. Multiplying by 5: 5d + d = 60, so 6d = 60 and d = 10 km. Total distance = 10 + 10 = 20 km traveled, but the question asks for "the distance travelled by her" in each direction, which is 10 km. Option D is correct.