Final answer:
The average speed on the return trip is 22/9 miles per hour.
Step-by-step explanation:
To find the average speed on the return trip, we need to divide the total distance of the return trip by the total time it took. The total distance is the same as the distance to the friend's house, which is 5 1/2 miles. The total time is 2 1/4 hours. To divide fractions, we need to multiply the first fraction by the reciprocal of the second fraction. So, 5 1/2 divided by 2 1/4 is equal to (11/2) divided by (9/4). We can simplify this by multiplying the numerator and denominator of the first fraction by 4, and the numerator and denominator of the second fraction by 2. Cancelling out common factors of 2, we get (11/2) x (4/9), which equals 44/18. Simplifying this fraction further, we get 22/9. Therefore, the average speed on the return trip is 22/9 miles per hour.