Heather left the mall traveling 16 mph. Then, 3 hours later, Carolyn left traveling the same direction at 28 mph. How long until Carolyn catches up with Heather?

Answer: it will take 7 hours before until Carolyn catches up with Heather.

Step-by-step explanation:

By the time Carolyn catches up with Heather, they would have travelled the same distance.

Heather left the mall traveling 16 mph. Let t represent the time that she spent in travelling this distance.

Distance = speed * time

Distance travelled by Heather would be

16 * t = 16t

Then, 3 hours later, Carolyn left traveling the same direction at 28 mph. Time spent by Carolyn in travelling the same distance would be (t - 3) hours

Distance travelled by Carolyn would be

28 (t - 3 = 28t - 84

Since the distance travelled is the same, then

16t = 28t - 84

28t - 16t = 84

12t = 84

t = 84/12 = 7