Upon the withdrawal of a county or counties from a library system, the disposal of assets shall be as follows:
When
A = Total library ad valorem tax and other local revenues received by the system during the service period
B = Total of such revenues derived from the withdrawing area during the service period
C = Net appraised value of system assets acquired during the service period less assets purchased with funds received from sources other than ad valorem tax and local revenues.
Then
B
A × C = withdrawing area's share of system assets which were acquired during the service period
Okla. Admin. Code § 405:10-7-6