Answer: it will take 7 hours until Corey catches up with David
Explanation:
At the time David catches up with Corey, they would have travelled the same distance. Let x represent this distance.
Distance = speed × time
Let t represent the time that David takes to cover x miles. David left the park traveling 16 mph. Therefore,
x = 16 × t = 16t
Then 3 hours later, Corey left traveling the same direction at 28 mph. It means that total time spent by Corey in travelling x miles is t - 3.
Distance travelled by Corey in (t - 3) hours would be
28(t - 3)
Since the distance covered is the same, then
16t = 28t - 84
28- 16t = 84
12t = 84
t = 84/12
t = 7 hours