Answer:
The speed of the boat in calm water is 12.8 miles per hour.
Explanation:
While going downstream the speed of the boat is "x + 2", where x is the speed in calm water, while going upstream the speed of the boat is "x - 2". He made a trip that had two legs, each with a distance of 50 miles, therefore, the sum of the times it took him to complete each leg must be equal to the total time of the trip.

For the upstream:

For the downstream:

The sum of each of these times must be equal to "8 h", therefore:

Since the speed can't be negative in this context, the only possible answer is 12.812 mph.