Sage Company is operating at 90% of capacity and is currently purchasing a part used in its manufacturing operations for $18.00 per unit. The unit cost for the business to make the part is $21.00, including fixed costs and $12.00, excluding fixed costs. If 38,915 units of the part are normally purchased during the year but could be manufactured using unused capacity, what would be the amount of differential cost increase or decrease from making the part rather than purchasing it?

a.$233,490 cost decrease

b.$116,745 cost increase

c.$233,490 cost increase

d.$700,470 cost decrease