<prompt> Translate the following text to EnglishMfano huu umebuniwa kuamua wastani wa gharama ya kitengo kama kazi ya kiasi Q kulingana na muundo wa gharama za USPS kwa mwaka wa fedha wa 1999.  <response>: The model is designed to define average unit cost as a function of volume Q, based on the USPS cost structure for FY 1999. 