Sec. 13. (a) As used in this chapter, "state income tax base period amount" means the aggregate amount of state adjusted gross income taxes paid or remitted by or on behalf of:
(1) employees employed within a district with respect to wages and salary earned for work in the district; and
(2) residents living within the district;
for the calendar year in which the district was established under this chapter, as determined by the department.
(b) If an individual is a resident of one (1) district and is employed within another district during a calendar year, the state income tax for the individual shall be attributed to the district in which the individual resides.