cant figure out processing time and waiting time

A US. Postal Semice supervisor is locking for ways to reduce stress in the sorting dopartment. With the exating arrangemont, stamped letters are machine-canceled and loaded into tubs with 325 latters per tub. The tubs are then pushed to postal clerks, who read and key zip codes into an automalod sorting machine at the rate of one tub per 425 seconds. To overcome the stress caused. when the stamp canceing machine outpaces the sorting clerks, a pull system is proposed. When the clerks are ready to process another tub of mal, they wil pull the fub from the canceing machine area. How many tibs should circulate between the sorting decks and the canceing machine it 75,000 inters are to be sorted during a 10 -hour shit, the safety stock policy yariable, a, is 0 . io, and the average wating time plus material handing time is 45 minutes per tub? The average processing time per tub of leters, p. is day. (Enter your response rounded to four decimal places) The average waiting time per kub of letters, w, is day. (Enter your reaponse roundod to four decimal places.) Therelore, the mumber of tubs that should circulate betaen the sorting decks and the canceling machine is tubs. (Enter your response rounded up to the next whote number.)