Task: Question Answering
Input (English): Problem: two bullet trains of equal lengths take 10 seconds and 20 seconds respectively to cross a telegraph post . if the length of each bullet train be 120 metres , in what time ( in seconds ) will they cross each other travelling in opposite direction ? 
Options: a ) 11 sec . , b ) 15 sec . , c ) 13.3 sec . , d ) 17 sec . , e ) 19 sec .
Output (English): c