<prompt> Translate the following text to EnglishKwa mfano, kwa ajili ya kipimo cha kiwango cha kurudi kwa kazi ya utoaji wa posta ya Marekani, kwanza tunaamua gharama ya jumla ya utoaji iliyotolewa na Huduma ya Posta.  <response>: We measure the returns to scale in the U.S. postal delivery function by first determining the total cost of delivery provided by the Postal Service. 