Exercise $3.$ Suppose users share a $2$ Mbps link. Also suppose that each user transmits only for $20\%$ of the time at $100$kbps$,$ and is idle the remaining time. $1.$ When circuit$-$switching is used, how many users can be supported? $=2.$ For the remaining of the problem, assume packet$-$switching. $($i$)$ Find the probability that a given user is transmitting. $($ii$)$ Suppose there are N $=40$ users. What is the probability that at any given time exactly n users transmit simultaneously? $($iii$)$ What is the probability that there are $21$ or more users transmitting simultaneously?