Answer:
Maisie is 22680 hours old.
Explanation:
Given is: Maisie is exactly 135 weeks old. 
First, lets calculate the number of hours in 1 week.
Number of hours in 1 day = 24
Number of hours in 7 days or 1 week = 
 hours
 hours
Now, number of hours in 135 weeks = 
 hours
 hours
Therefore, Maisie is 22680 hours old.