English to Spanish Bus/Financial Business/Commerce (general)

Hello everybody, can you help me translate "aggregate extension" into Spanish? I cannot figure out if Aggregate is an adjective or a noun here.

For the 2018 levy year the approximate amount of the additional tax extendable against property containing a single family residence and having a fair market value at the time of the referendum of $100,000 is estimated to be $23.33.
If the proposition is approved, the AGGREGATE EXTENSION for 2018 will be determined by the limiting rate set forth in the proposition, rather than the otherwise applicable limiting rate calculated under the provisions of the Property Tax Extension Limitation Law.

Thank you!