CREATE TABLE table_25025 ("District" TEXT, "Vacator" TEXT, "Reason for change" TEXT, "Successor" TEXT, "Date successor seated" TEXT)

How many seats became avaliable in Massachusetts 3rd district?
SELECT COUNT("Vacator") FROM table_25025 WHERE "District" = 'Massachusetts 3rd'
SELECT COUNT("Vacator") FROM "table_25025" WHERE "District" = 'Massachusetts 3rd'