Task: Question Answering
Input (English): Problem: two trains leave a station traveling in the same direction . train a leaves traveling at a constant speed of 50 mph , while train b leaves traveling at a constant speed of 80 mph . if train b left the station 30 minutes after train a left , in how many minutes will train b overtake train a ? 
Options: a ) 30 , b ) 40 , c ) 50 , d ) 60 , e ) 70
Output (English): c