The average speed of a train that travels x miles in 3/4 hour

Average speed of train = 4x/3 miles per hour

Step-by-step explanation:

A train travels x miles in 3/4 hours

Let's find the distance train travels in 1 hour.

i. e distance travel in one hour = x / (3/4)

or distance travel in one hour = 4x/3

So,

Average speed of train = distance / time

Average speed of train = (4x/3 / 1)

Average speed of train = 4x/3 miles per hour