Task: Question Answering
Input (English): Problem: if a farmer sells 5 of his goats , his stock of feed will last for 4 more days than planned , but if he buys 10 more goats , he will run out of feed 3 days earlier than planned . if no goats are sold or bought , the farmer will be exactly on schedule . how many goats does the farmer have ? 
Options: a ) 12 , b ) 20 , c ) 48 , d ) 55 , e ) 60
Output (English): b