15-31-311. Sales factor for sales in this state. (1) Sales of tangible personal property are in this state if:
(a) the property is delivered or shipped to a purchaser, other than the United States government, within this state regardless of the f.o.b. point or other conditions of the sale; or
(b) the property is shipped from an office, store, warehouse, factory, or other place of storage in this state and:
(i) the purchaser is the United States government; or
(ii) the taxpayer is not taxable in the state of the purchaser.
(2) Sales, other than sales of tangible personal property, are in this state if:
(a) the income-producing activity is performed in this state; or
(b) the income-producing activity is performed both in and outside this state and a greater proportion of the income-producing activity is performed in this state than in any other state, based on costs of performance.