Task: Question Answering
Input (English): Problem: in an election between two candidates a and b , the number of valid votes received by a exceeds those received by b by 15 % of the total number of votes polled . if 20 % of the votes polled were invalid and a total of 9720 votes were polled , then how many valid votes did b get ? 
Options: a ) 1888 , b ) 2999 , c ) 3159 , d ) 2777 , e ) 2991
Output (English): c