<prompt> Translate the following text to Swahilithe cost of delivery and the benefits received by the mailer, the letter-size piece might be a more efficient piece for the nation as a whole, but the mailer will not make the change unless a rate differential is offered.  <response>: Kwa sababu ya gharama za utoaji na faida zinazopokelewa na mjumbe, kipande cha ukubwa wa barua inaweza kuwa kipande cha ufanisi zaidi kwa taifa nzima, lakini mjumbe hatabadilisha isipokuwa tofauti ya kiwango inapatikana. 