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?
Choose the correct choice from the following answers:  A) 1/2  B) 2  C) 1  D) 4  E) 5
d = rt   M: r = 40 mph, t = t + 1/4hr   d = 40 (t + 1/4)   P: r = 60, t = t   d = 60t   since they went the same distance:   40t + 40/4 = 60t   20t = 40/4   t = 1/2 or 1/2 hr   1/2
<result>A</result>
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?