(a) The association, in determining the proportionate amount to be paid by individual insurers under an assessment under Section 462.160, shall consider the lines of business written by the impaired insurer and shall assess individual insurers in proportion to the ratio that the total net direct written premiums collected in this state by the insurer for those lines of business bears to the total net direct written premiums collected by all insurers, other than impaired insurers, in this state for those lines of business.
(b) The association shall determine the total net direct written premiums of an individual insurer and of all insurers in the state from the insurers' annual statements for the year preceding assessment.