text: One can easily increase the discount from zero and , for each discount level , calculate several ( 1 ) the total revenue lost by the postal service , which is simply equal to the discount level multiplied by the presort volume ; ( 2 ) the total cost incurred by mailers or by mailing organizations , which is the area under the supply curve ; and ( 3 ) the total savings of the postal service because it does not have to do the sorting and processing , which is the area under the cost curve .
  
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  They are able to increase the discount from zero with ease .