Suppose that Anshul paddles the boat for p km and swims for s km.
Since Anshul leaves the boat in the lake and it does not move,
\Sonali swims p km and paddles the boat for s km.
Note that each paddles at 10 km/h and each swims at 3 km/h and each takes exactly 120 minutes (or 2 hours) to complete the trip.
If s<p, then Anshul would paddle farther and swim less distance than Sonali and so would reach the other side in less time than Sonali.
If s>p, then Sonali would paddle farther and swim less distance than Anshul and so would reach the other side in less time than Anshul.
Since, they each take 120 minutes,
\we must have s = p.
The boat is not being paddled for the period of time from when Anshul stops paddling to the time when Sonali stops swimming, which is a period of 92.31 – 27.69 = 64.62 minutes.
Hence, option c. is correct.