Question 4 [20 pts] Suppose users share a 3 Mbps link through circuit switching. Also suppose each user requires 150 kbps when transmitting, but each user transmits only 10 percent of the time.

a) [5] How many users can be supported?

b) [5] Find the probability that a given user is transmitting.

c) [5] Suppose there are 120 users. Find the probability that at any given time, exactly n users are transmitting simultaneously.

d) [5] Find the probability that this circuit-switching link cannot transmit data from the users (probability of failure)