<prompt> Translate the following text to EnglishGharama kwa kila shughuli ya posta kusindika barua, utoaji, nk ambayo inaweza kuhusishwa na kiasi cha barua, imegawanywa na kiasi cha jumla ili kupata makadirio ya gharama ya kiwango.  <response>: Costs for each postal activity mail processing, delivery, etc that can be attributed to mail volumes, are divided by total volume to obtain an estimate of the marginal cost. 