Let's answer this question step by step
Distance = d= 25 miles
Average speed = s = 10 miles/hour
The time it takes to reach Lake Kegonsa = t
Now,
d/t=s
d/s=t
Hence, t=25/10
t=2.5 hours
According to our caluclutions:
08:30 A.M is the latest time they can leave the park in order to arrive at the lake by 11 A.M.