<prompt> Translate the following text to EnglishUwezo wa gharama kwa kiasi kwa ajili ya mfumo wa posta inaweza kuchunguzwa moja kwa moja zinazotolewa uwiano wa gharama za kudumu kwa kubadilika ni inayojulikana kwa kazi.  <response>: The sensitivity of cost to volume for a postal system can be investigated directly provided the ratio of fixed to variable costs is known by function. 