<h2>
Answer:</h2>
The time taken by them to be 54 miles apart is: 4.5 hours
<h2>
Step-by-step explanation:</h2>
Let it takes t hours for both the boats such that they are 54 miles apart.
The northbound boat travels 4 miles per hour.
Hence, the distance traveled by the northbound boat is: 4t miles.
( since the distance is the product of speed and time.
i.e.
Distance=Speed×Time)
The speed of the southbound boat is: 8 miles per hour.
This means that the distance traveled by this boat in t hours is: 8t miles
Hence, the total distance between the two boat in t hours is:
4t+8t=54
i.e.
12t=54
i.e.
t=54/12
i.e.
t=4.5 hours
Hence, the answer is: 4.5 hours
