RCW 15.21.040: Combination sales.

When one or more items are offered for sale or sold with one or more items at a combined price, or offered individually or as a package or a unit to be given with the sale of one or more items, each and all such items shall for the purpose of this chapter be deemed to be offered for sale, and as to such transaction the cost basis shall be the combined cost basis of all such items as determined pursuant to RCW 15.21.030.