Task: Question Answering
Input (English): Problem: pipe a that can fill a tank in an hour and pipe b that can fill the tank in half an hour are opened simultaneously when the tank is empty . pipe b is shut 10 minutes before the tank overflows . when will the tank overflow ? 
Options: a ) 37 mins , b ) 35 mins , c ) 40 mins , d ) 32 mins , e ) 36 mins
Output (English): a