Task: Question Answering
Input (English): Problem: mary passed a certain gas station on a highway while traveling west at a constant speed of 40 miles per hour . then , 15 minutes later , paul passed the same gas station while traveling west at a constant speed of 60 miles per hour . if both drivers maintained their speeds and both remained on the highway for at least 2 hours , how long after he passed the gas station did paul catch up with mary ? 
Options: a ) 1 / 2 , b ) 2 , c ) 1 , d ) 4 , e ) 5
Output (English): a