please help

A U.S. Postal Service suporvisor is looking for ways to reduce stress in the sorting tepertment. With the existing arrangement, stamped letters are machine-canceled and lasded inta bubs with 350 letters per tub. The tubs are thon punhed to postal clerks, who road and koy zip codes into an outoenated corting machine at the rato of one tub per 250 seconds. To overoome the stress caused when the stamp canceling machine outpaces the sorting dorks, a pull systom is proposed. Whon the clorks are roody to process another tub of mal, they will pull the fub from the canowing miechine area. How many tubs should circulate betwoen the sorting clerks and the canceling machine if 75 , 000 letters are to be sarted during a 12 hour shit, the salety stock policy variable, a, is 0.25 , and the average wailing time plus material handing time is 20 mirutes per buth? The averoge processing time per tub of letters, p1 is day. (Enter your responso roundod to four docimal places) The average wakng bene per tub of letters, w, la dyy (Enter your response roundod fo four docimbl places). Therefore, the number of tubs that should eiculate between the sorting derks and the canceling machine is tubs. (Enteir your rosponse rounded up to the next whole number.)