Task: Question Answering
Input (English): Problem: two trains start from p and q respectively and travel towards each other at a speed of 50 km / hr and 40 km / hr respectively . by the time they meet , the first train has travelled 100 km more than the second . the distance between p and q is : 
Options: a ) 500 km , b ) 630 km , c ) 900 km , d ) 660 km , e ) none
Output (English): c