The business income of a combined group is determined as follows:
(a) From the total income of the combined group, determined under subsection (b) of this section, subtract any income and add any expense or loss, other than the business income, expense or loss of the combined group.
(b) Except as otherwise provided, the total income of the combined group is the sum of the income of each member of the combined group determined under federal income tax laws, as adjusted for state purposes, as if the member were not consolidated for federal purposes. The income of each member of the combined group shall be determined as follows:
(1) For any member incorporated in the United States, or included in a consolidated federal corporate income tax return, the income to be included in the total income of the combined group shall be the taxable income for the corporation after making allowable adjustments under this article.