Task: Question Answering
Input (English): Problem: two bullet trains of equal lengths take 10 seconds and 30 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 ) 13 sec . , b ) 14 sec . , c ) 12 sec . , d ) 15 sec . , e ) 19 sec .
Output (English): d