Persons engaged in business both within and without the city, or partially within and partially without the city, and maintaining an office or place of business within the city and not elsewhere shall be taxable on the gross income from the business without regard to the place where such business is transacted; and such persons having an office or place of business inside the city and also elsewhere and such persons engaged in business within the city but without an office or place of business within the city shall, for the purpose of computing tax liability under this chapter, apportion to the city that portion of his gross income which is derived from business transacted within the city. Where such apportionment cannot be made by separate accounting methods, the taxpayer shall apportion to the city that portion of his total income which the cost of doing business within the city bears to the total cost of doing business within and without the city.

Persons maintaining an office, plant, warehouse or other business establishment which is partly within and partly outside of the city shall be taxable on gross proceeds of sales, or gross income of the business, attributable to business within the city, ascertained either (1) by a segregation of business within and business without the city, shown and supported by separate account records, of (2) if such segregation cannot be practicably made, by apportionment to the city of that part of the gross proceeds of sales, or gross income of the business, derived from business both within and outside the city (a) in the proportion that the cost of doing business within the city bears to the cost of doing business both within and outside the city, or (b) when the use of such apportionment factor is impractical or inequitable, by a fair and equitable apportionment of such values, proceeds or income between business within the city and business outside the city upon such basis, comparable in character to that prescribed in (a) above, as shall be agreed upon by the Director of Financial & Management Services and the taxpayer after consideration of the facts; provided, in the case of financial institutions upon which the business and occupation tax is imposed by this chapter and which are engaged in business both within and without the city, such computation shall be pursuant to rules promulgated by the Washington State Department of Revenue as contemplated by Section 3 of Chapter 134, Laws of Washington, 1972. (Ord. M-1998 §3, 1979: Ord. M-1693 §2, 1976: Ord. M-1329 §2, 1972: Ord. M-203 §5, 1954)