Task: Question Answering
Input (English): Problem: if the difference between compound interest ( interest compounded yearly ) and simple interest on a certain sum at the rate 20 % p . a . after 3 years is rs . 1280 then what is the principal ? 
Options: a ) 7900 , b ) 8,000 , c ) 10,000 , d ) 8,300 , e ) 9,300
Output (English): c