Task: Question Answering
Input (English): Problem: joan took out a mortgage from hel local bank . each monthly mortgage payment she makes must be triple the amount of the previous month ' s payment . if her first payment is $ 100 , and the total amount she must pay back is $ 12100 , how many months will it take joan to pay back her mortgage ? 
Options: a ) 6 , b ) 8 , c ) 10 , d ) 5 , e ) 13
Output (English): d