Sheffield, Inc. can produce 100 units of a component part with the following costs $30800 Direct Materials Direct Labour 13000 Variable Overhead 31100 Fixed Overhead 21400 Sheffield Inc. purchases the units externally for $81000, by what amount will its total costs change? Fixed cants are not avoidable the company purchases externally a decrease of $ 21400 an increase of $ 6100 an increase of $17800 an increase of 581000