Task: Question Answering
Input (English): Problem: two trains start simultaneously from opposite ends of a 180 - km route and travel toward each other on parallel tracks . train x , traveling at a constant rate , completes the 180 - km trip in 5 hours . train y , travelling at a constant rate , completes the 180 - km trip in 4 hours . how many kilometers had train x traveled when it met train y ? 
Options: a ) 72 , b ) 74 , c ) 76 , d ) 78 , e ) 80
Output (English): e