Task: Question Answering
Input (English): Problem: mary is expected to pay back a total sum of $ 819200 to her bank as mortgage . if she is expected to make a payment which is double of the previous months amount , how long will it take her to fully repay the loan if her initial payment was $ 400 . 
Options: a ) 13 , b ) 15 , c ) 12 , d ) 10 , e ) 11
Output (English): e