Answer:
It may be 3 : 45.
Explanation:
Ross started walking his dog at 3 : 15 and finished before 4 : 00.
Therefore, there is a gap of 45 minutes between 3 : 15 and 4 : 00.
So, Ross walked with his dog for less than 45 minutes.
Therefore, Ross could have finished walking his dog at any time before 4 : 00 and it may be 3 : 45. (Answer)