According to faq.usps.com, "Pieces going to a domestic location may not measure more than 108 inches in length and girth combined. There is an exception with USPS Retail Ground, where the maximum is 130 inches." This is a common optimization problem in many calculus textbooks. To solve it, we find the largest possible rectangular parcel that can be shipped under these conditions. We do this by defining a volume function in terms of another variable, in this case the width. We then differentiate the function with respect to that variable, and set it to zero. Solving, we find the dimensions needed to achieve maximum volume under the conditions. https://en.wikipedia.org/wiki/United_States_Postal_Service learn.play.solve@gmail.com