$"5-13$ Marc Hernandez's construction firm currently has three projects in progress. Each requires a specific supply of gravel. There are three gravel pits available to provide for Hernandez's needs, but shipping costs differ from location to location. The following table summarizes the transportation costs:

$\backslash$table$[[,$To$,,,],[$From$,$Job $1,$Job $2,$job $3,$Tonnage Allowance$],[$Central pit,$$9,$$$8,57,3,000],[$Rockpt$,$$$7,$$$11,$$$6,4000],[$Acme pit,$$4,$$$3,$$$12,6000],[$Job reguirements $($tons$),2500,3750,4850,]]$

$($a$).$ Determine Hernandez's optimal shipping quantities so as to minimize total transportation costs."