Your final choice could be a matter of personal Taste. Many sources describing US Public debt I've checked on side strictly with FEDERAL (without state/local added) DEBT.
(My view) I reviewed the Fed. STL "offerings." If your assignment requires you to use that as a primary source, then those offerings seem to have a site preference of adding (not subtracting) State and Local numbers to Fed totals. To play it safe, provide notice when submitting the case (or if safe to do so beforehand, talk to the instructor) that this site's above mentioned "State-Local included" disclosures of data measurement and what comprises the data made sense to you, helped as a guiding light in tackling the case. (PS I am using my Fed-State-Local reports assessment knowledge from past work with DC-based Governmental Accounting non-profit, to make the above "view").