Q$4.($Inventory Buildup & Little's Law$).$ McDonald's at Coit and Turnpike is operating from $9$am to $5$ pm$.$ The restaurant can serve up to $100$ customers per hour. Customers arrive at the rate $120$ customers $/$ hour during the hours $9-11$am to grab McMorning, $200$ customers $/$ hour pour in during the peak hours of $11$ am to $1$ pm$,$ and for the lazy afternoon hours until the restaurant closes, only $20$ customers walk in per hour.$($b$)$ What is the average number of people waiting throughout the day? $(3$ point$)($c$)$ What is their average waiting time? $(3$ point$)$