Signa Corporation currently manufactures 17,000 staplers annually for its main product. The are as follows: Direct materials $ 2.50 Direct labour 7.50 Variable overhead 3.00 Fixed overhead 8.00 Total $21.00 Darsel Company has contacted Signa with an offer to sell it 17,000 staplers for $19.00 each. 58 of the fred overhead per unit is unavoidable. Prepare an incremental analysis for the make-or-buy decision