Task: Question Answering
Input (English): Problem: two trains start simultaneously from opposite ends of a 150 - km route and travel toward each other on parallel tracks . train x , traveling at a constant rate , completes the 150 - km trip in 4 hours . train y , travelling at a constant rate , completes the 150 - km trip in 3.5 hours . how many kilometers had train x traveled when it met train y ? 
Options: a ) 68 , b ) 70 , c ) 72 , d ) 74 , e ) 76
Output (English): b