The ticket booth on the Tech campus is operated by one person, who is selling tickets for the annual Tech versus State football game on Saturday. The ticket seller can serve an average of $15$ customers per hour; on average, $13$ customers arrive to purchase tickets each hour $($Poisson distributed$).$

a$)$ Calculate W$,$ Wq$,$ L$,$ Lq

b$)$ What percentage of the time is the ticket booth operator actively engaged in selling tickets?