As used in this chapter, "full-time equivalent basic education certificated instructional employee" means the full-time equivalent calculated pursuant to WAC 392-121-215 for:

(1) A basic education certificated instructional employee as defined in WAC 392-121-210; and

(2) A special education certificated instructional employee, in program 21, as determined by the following:

(a) The total special education, program 21, certificated instructional staff assigned to grades kindergarten through twelve;

(b) Times the annual percentage used in determination of a district's 3121 revenue—the special education cost accounting method required pursuant to section 507 (2)(b) of the 2007 supplemental operating budget.