Q # $2$ Consider a cellular system with a cluster size of $7$ such that each cell has $90$ voice channels. If there is a user density of $9000$ users $\frac{?}{K{m}^2}$ in the system, and each user makes an average call of one call per hour and each call lasts one minute during peak hour. Using Erlang $C$ model, determine the probability that a user will experience a delay greater than $20$ seconds if all calls are queued?

Points: $\{15\}$