For the purpose of Section 209.022, the rate of insured unemployment is computed by:
(1) dividing:
(A) the average weekly number of individuals filing claims for regular compensation in this state for weeks of unemployment with respect to the most recent 13-consecutive-week period, as determined by the commission from the commission's reports to the secretary; by
(B) the average monthly employment covered under this subtitle for the first four of the most recent six completed calendar quarters ending before the end of the 13-week period; and
(2) multiplying the quotient by 100 to determine a percentage rate.