d = 25 miles, the distance driven
t = 30 minutes, the time taken for the drive.
In SI units,
1 mile = 1609 meters.
Also,
1 minute = 60 seconds.
Therefore
d = (25 mi) * (1609 m/mi) = 40225 m
t = (30 min) * (60 s/min) = 1800 s
By definition, the average speed is
v = d/t
= (40225 m)/(1800 s)
= 22.3472 m/s
Answer: 22.35 m/s (nearest hundredth)