Answer:
Add the information, and find the second number.
Explanation:
"She throws them 8.49 m/s high"
8.49 + ? = ?
"Her friend catches them 2.89 m/s higher"
8.49 - 2.89 = 5.60
The reason why you must subtract is because it is asking how high it is in the air, going up and down.
8.49 + 5.60 = ?
8.49 + 5.60 = 14.09
Which means, it was in the air for 14.09 m/s.