Task: Question Answering
Input (English): Problem: two trains running in opposite directions cross a man standing on the platform in 27 seconds and 17 seconds respectively . if they cross each other in 21 seconds , what is the ratio of their speeds ? 
Options: a ) 1 : 3 , b ) 3 : 1 , c ) 2 : 3 , d ) 3 : 2 , e ) 3 : 4
Output (English): c