Suppose users share a $3$Mbps link. Also suppose each user requires $150$ kbps when transmitting, but each user transmits only $10\%$ of the time.a$.$ When circuit switching is used, how many users can be supported?b$.$ Fortheremainderofthisproblem,supposepacketswitchingisused.Findtheprobability that a given user is transmitting.c$.$ Suppose there are $120$ users. Find the probability that any given time, exactlyn users are transmitting simultaneously. $($Hint: use the binomial distribution.$)$d$.$ Findtheprobabilitythatthereare$21$ormoreuserstransmittingsimultaneously.