he United States Post Office offers three sizes of priority mail flat rate boxes: small, medium, and large. Let X1?,X2?, and X3? be the number of small, medium, and large priority mail flat rate boxes shipped during a given week by a small business. We know that: ?1?=50,?2?=70, ?3?=20,?1?=10,?2?=12,?3?=6. It costs $8.25 to ship a small flat rate box, $14.25 to ship a medium flat rate box, and $21.50 to ship a large flat rate box. a) Calculate the expected total cost of shipping small, medium, and large boxes per week. (Answer for each size separately.) b) Calculate the variance in cost of shipping small, medium, and large boxes per week. (Answer for each size separately.)