Mo. Rev. Stat. § 92.160

The earnings or net profits subject to tax of any nonresident individual, of any association or business conducted by nonresidents, or of any corporation, in any case in which the work done, services performed or rendered, and business or other activities conducted are done, performed, rendered or conducted both within and without the city may be ascertained by formulae set forth in any ordinance enacted pursuant to sections 92.110 to 92.200 or prescribed by rules or regulations adopted pursuant to such ordinance.