Hello,
The answer would be about "8-9 hours of sleep per day".
Reason:
At that age the body is growing therefore the body would need more energy to grow so thats why the amount of sleep would increase because adults, and teenagers would be into more physical activities and work that would drain his or her energy therefore they should get to 8-9 hours of sleep in order to last the person the whole day.
If you need anymore help feel free to ask me!
Hope this helps!
~Nonportrit