It is very important to go through all the details that have been provided in the question. These information's will come in very handy while getting to the solution for the answer. Now let us concentrate on the problem in hand.
Distance between Bristol and Rome that the plane covers = 1200 miles
Starting time of the plane from Bristol = 14:00 hrs
Landing time of the plane in Rome = 17:15 hrs
Then
Total time taken by the plane to travel from Bristol to Rome = 17:15 - 14:00 hours
= 3 .15 hours
So
The average speed of the plane = 1200/3.15 miles per hour
= 380.95 miles per hour
From the above deduction we can conclude that the average speed of the plane traveling from Bristol to Rome is 380.95 miles per hour.
