Missouri Revised Statutes Title X. Taxation and Revenue § 143.041. Nonresident individual--inapplicable to out-of-state businesses and employees, when

1. A tax is hereby imposed for every taxable year on the income of every nonresident individual which is derived from sources within this state. The tax shall be that amount which bears the same ratio to the tax applicable to the individual if he would have been a resident as (A) his Missouri nonresident adjusted gross income as determined under section 143.181 (Missouri adjusted gross income derived from sources within this state) bears to (B) his Missouri adjusted gross income derived from all sources.

2. The provisions of this section shall not apply to out-of-state businesses or out-of-state employees operating under sections 190.270 to 190.285.