This tax shall be determined by establishing a ratio of the unrelated business taxable income to the bookstore's gross income as defined by the Internal Revenue Code. That percent shall be the maximum percentage of such bookstore property on which a property tax can be levied.
At the end of a fiscal year when unrelated business income has been generated, the nonprofit organization shall file with the assessor copies of the organization's most recent tax return filed with the Internal Revenue Service.
Ca. Rev. and Tax. Code § 202