(a) Gross receipts from transactions other than sales of tangible personal property (including transactions with the United States government) are attributed to this state if the income producing activity which gave rise to the receipts is performed wholly within this state. Also, gross receipts are attributed to this state, if, with respect to a particular item of income, the income producing activity is performed within and without this state but the greater proportion of the income producing activity is performed in this state, based on costs of performance. The term "income producing activity" applies to each separate item of income and means the transactions and activity directly engaged in by the taxpayer in the regular course of its trade or business for the ultimate purpose of obtaining gains or profit. Such activity does not include transactions and activities performed on behalf of a taxpayer, such as those conducted on its behalf by an independent contractor. Accordingly, income producing activity includes but is not limited to the following:
(1) The rendering of personal services by employees or the utilization of tangible and intangible property by the taxpayer in performing a service. (2) The sale, rental, leasing, licensing or other use of real property. (3) The rental, leasing, licensing or other use of tangible personal property. (4) The sale, licensing or other use of intangible personal property. The mere holding of intangible personal property is not, of itself, an income producing activity.
The term "costs of performance" means direct costs determined in a manner consistent with generally accepted accounting principles and in accordance with accepted conditions or practices in the trade or business of the taxpayer.