Assume that two years have passed, and the purchasing agent mentioned in Problem 22 must recompute the optimal number of wafers to purchase and from which source to purchase them. Source B has decided to accept any size offer, but sells the wafers for $2.55 each for orders of up to 3,000 wafers and $2.25 each for the incremental amount ordered over 3,000 wafers. Source A still has the same price schedule, and Source C went out of business. Now which source should be used?