(1) Each component city or town shall pay such proportion of the supplemental income to the authority as determined by either one of the following prescribed methods or by a combination of fifty percent of one and fifty percent of the other as provided in subsection (1)(c) of this section:

(a) Each component city or town shall pay such proportion of the supplemental income as the assessed valuation of property within its limits bears to the total assessed valuation of taxable property within the activated authority.

(b) Each component city or town shall pay such proportion of the supplemental income as the total population of such city or town bears to the total population of the activated authority. The population of the city or town shall be determined by the most recent census, estimate or survey by the federal bureau of census or any state board or commission authorized to make such a census, estimate or survey.

(c) A combination of the methods prescribed in (a) and (b) of this subsection: PROVIDED, That such combination shall be of fifty percent of the method prescribed in (a) of this subsection and fifty percent of the method prescribed in (b) of this subsection.

(2) Each component county shall pay such proportion of such supplemental income to the authority as determined by either one of the following prescribed methods or by a combination of fifty percent of one and fifty percent of the other as prescribed in subsection (2)(c) of this section:

(a) Each component county shall pay such proportion of such supplemental income as the assessed valuation of the property within the unincorporated area of such county lying within the activated authority bears to the total assessed valuation of taxable property within the activated authority.

(b) Each component county shall pay such proportion of the supplemental income as the total population of the unincorporated area of such county bears to the total population of the activated authority. The population of the county shall be determined by the most recent census, estimate or survey by the federal bureau of census or any state board or commission authorized to make such a census, estimate or survey.

(c) A combination of the methods prescribed in (a) and (b) of this subsection: PROVIDED, That such combination shall be of fifty percent of the method prescribed in (a) of this subsection and fifty percent of the method prescribed in (b) of this subsection.

(3) In making such determination of the assessed valuation of property in the component cities, towns and counties, the board shall use the last available assessed valuations. The board shall certify to each component city, town and county, prior to the fourth Monday in June of each year, the share of the supplemental income to be paid by such component city, town or county for the next calendar year. The latter shall then include such amount in its budget for the ensuing calendar year, and during such year shall pay to the activated authority, in equal quarterly installments, the amount of its supplemental share.