(a) A member may establish service credit in the elected class for any calendar year during any part of which:
(1) the member held an office included in that class; or
(2) the member was eligible to take the oath for an office included in that class.
(b) A member may establish credit under this section by depositing with the retirement system in a lump sum a contribution computed as provided by Section 813.404, plus interest computed at an annual rate of 10 percent from the fiscal year in which the service was performed to the date of deposit.