Only selections B and D give a maximum height of 13 at t=3. However, both of those functions have the height be -5 at t=0, meaning the ball was served from 5 ft below ground. This does not seem like an appropriate model.
We suspect ...
• the "correct" answers are probably B and D
• whoever wrote the problem wasn't paying attention.
Answer by JKismyhusbandbae: The mean is the average of all the numbers. You add all the numbers and divide by how many numbers you added to get the mean.
The correct answer ids 100% answer choice D
What's the question?
If it's "What's the difference?" or something like that, then the answer is 15. :)