Sec. 4. For a taxpayer filing a combined return for its unitary group, the group's apportioned income for a taxable year consists of:
(1) the aggregate adjusted gross income, from whatever source derived, of the members of the unitary group; multiplied by
(2) the quotient of:
(A) all the receipts of the taxpayer members of the unitary group that are attributable to transacting business in Indiana; divided by
(B) the receipts of all the members of the unitary group from transacting business in all taxing jurisdictions.