13. In the case of a municipal corporation whose territory is not included in that of the municipality which has jurisdiction in it, the notice of its aliquot share of the expenditures contemplated in section 10 shall be sent annually to it at the time agreed with the municipality, or, failing agreement, at the time fixed by the Commission.
The aliquot share is payable within ninety days of the date of sending.
The payment may be provided for in the budget for the fiscal period during which it must be made.