<prompt> Translate the following text to SwahiliThe postal revenue decreases by e of a cent times the 20 billion pieces, but the postal cost decreases by 4a time the 20 billion pieces.  <response>: Mapato ya posta hupungua kwa e ya senti mara 20 bilioni, lakini gharama za posta hupungua kwa mara 4a mara 20 bilioni. 