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 $$2\mathrm{.}55$ each for orders of up to $3,000$ wafers and $$2\mathrm{.}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?