Suppose users share a 2.4 Mbps link. Also suppose each user requires 300 kbps when transmitting. a) When circuit switching is used, how many simultaneous users can be supported over the 2.4 Mbps link? b) Suppose now that packet switching is used over the 2.4 Mbps link, that each user requires 450 kbps when transmitting, and that there are 21 users in total. Each user transmits with a 10% probability. Find the probability that at any given time instant, 4 or more users are transmitting simultaneously.