Task: Question Answering
Input (English): Problem: two trains , a and b , started simultaneously from opposite ends of a 120 - mile route and traveled toward each other on parallel tracks . train a , traveling at a constant rate , completed the 120 - mile trip in 6 hours ; train b , traveling at a constant rate , completed the 120 - mile trip in 4 hours . how many miles had train a traveled when it met train b ? 
Options: a ) 28 , b ) 36 , c ) 48 , d ) 50 , e ) 54
Output (English): c