Answer: The correct option is B, i.e., 40 miles per hour.
Explanation:
Let the speed of bus in the afternoon route be x.
From the given information the average speed is 12 miles per hour less than the afternoon route. So, the speed of bus in the morning route is x-12.
So,
Time taken by bus in morning route is,
Time taken by bus in afternoon route is,
Since it is given that the time is same, so
Since x represents the speed of bus in afternoon route, therefore the correct option is B, i.e., 40 miles per hour.