Task: Question Answering
Input (English): Problem: a gambler has won 40 % of his 30 poker games for the week so far . if , all of a sudden , his luck changes and he begins winning 80 % of the time , how many more games must he play to end up winning 60 % of all his games for the week ? 
Options: a ) 20 , b ) 25 , c ) 30 , d ) 35 , e ) 40
Output (English): c