CREATE TABLE table_77790 ("Year" FLOAT, "Division" FLOAT, "League" TEXT, "Reg. Season" TEXT, "Playoffs" TEXT, "Open Cup" TEXT)

How many years was there a team that was part of the usisl pro league?
SELECT COUNT("Year") FROM table_77790 WHERE "League" = 'usisl pro league'
SELECT COUNT("Year") FROM "table_77790" WHERE "League" = 'usisl pro league'