CREATE TABLE table_78240 ("Institution" TEXT, "City" TEXT, "State" TEXT, "Nickname" TEXT, "Joined" FLOAT, "Conference championships" FLOAT)

What is the latest year joined with a Conference championships of 5, and an Institution of university of north carolina?
SELECT MAX("Joined") FROM table_78240 WHERE "Conference championships" = '5' AND "Institution" = 'university of north carolina'
SELECT MAX("Joined") FROM "table_78240" WHERE "Conference championships" = '5' AND "Institution" = 'university of north carolina'