Starling Co. is considering disposing of a machine with a book value of $12,500 and estimated remaining life of five years. The old machine can be sold for $1,500. A new high-speed machine can be purchased at a cost of $25,000. It will have a useful life of five years and no residual value. It is estimated that the annual variable manufacturing costs will be reduced from $26,000 to $23,500 if the new machine is purchased. The total net differential increase or decrease in cost for the new equipment for the entire five years is:
a. decrease of $11,000
b. decrease of $15,000
c. increase of $11,000
d. increase of $15,000