It is given in the question that
The school is 625 meters far from Alex house. It took him 15 minutes to go from home to school, and run back to home in 10 minutes.
Total distance is 625 meters and total time taken is
[tex] (10+15) minutes=25minutes [/tex]
Average speed is
[tex] \frac{total \ distance \ travelled}{total \ time \ taken} [/tex]
[tex] = \frac{625}{25}meter/minute = 25 meter/minute [/tex]
