Answer:
Average day end balance using weighted average = $1,316.667
Average day end balance using simple average = $1,050
Step-by-step explanation:
Provided opening balance = $1,200
During the month addition in such balance = $500
New balance as on 16 November = $1,200 + $500 = $1,700
Further by the end of month of November balance after payment = $1,700 - $800
= $900
Thus, opening balance = $1,200
Closing = $900
Simple average = 
Day end balance = $1,050
For this weighted average can be done
First 15 days balance = $1,200 as no transaction was done.
From 16 to 25 November balance increased by $500 = $1,700 for 10 days
Remaining days = 5 days = $1,700 - $800 paid = $900
Using weighted average we have

Day end balance = $1,316.667