Answer:
90 miles per hour is the average speed.
Explanation:
The formula for Average Speed can be given as follows:

Here time taken is from 1 PM to 4 PM i.e.
Total Time taken = (4-1) hours = 3 hours
Also, it is given that the Total distance covered = 270 miles
As per the formula above:

So, answer is: 270 miles/ hour is the average speed of the train from Philadelphia to Boston.