Speed!

At 9am, John was cycling from Point A to Point B. At the same time, Mary was cycling from Point B to Point A using the same route as John. Cycling at a speed 4km/h faster than Mary, John would pass Mary 300m away from the midpoint.
(a) What time did they pass each other?
(b) If John took another 3 minutes to reach Point B, what time would Mary reach Point A?