M2 Collisons question

Hi there,
This question is worded so badly and I'm having trouble with it.
Two marbles, A and B, are placed along the diameter, either side of a circular groove and have equal mass. Both are at rest. A is is released from rest and hits b 2s later.The coefficant of restitution is 0.5.
(a). Find the time between the first collision and when B collides with A.
(b). find the total number of collisions in the first 5 minutes.

Please help, thank you!