Alright, lets get started.
![t_{i} = 11:31 am](https://tex.z-dn.net/?f=%20t_%7Bi%7D%20%20%3D%2011%3A31%20am%20)
![t_{f} = 8:22 pm](https://tex.z-dn.net/?f=%20t_%7Bf%7D%20%3D%208%3A22%20pm%20)
We need to find elapsed time between 11:31 am and 8:22 pm.
From 11:31 am, it will first go to 12:00 pm then 8:22 pm.
So, time elapsed from 11:31 am to 12:00 pm :
![12:00 - 11:31 = 0 : 29](https://tex.z-dn.net/?f=%2012%3A00%20-%2011%3A31%20%3D%200%20%3A%2029%20)
time elapsed from 12:00 pm to 8:22 pm : 8:22
So total time elapsed : ![0:29 + 8 :22](https://tex.z-dn.net/?f=%200%3A29%20%2B%208%20%3A22%20)
So total time elapsed : 8 : 51 : Answer
Hope it will help :)