CREATE TABLE table_18251 ("District" TEXT, "Incumbent" TEXT, "Party" TEXT, "First elected" FLOAT, "Result" TEXT, "Candidates" TEXT)

who is the incumbent with candidates being tom ridge (r) 80.9% joylyn blackwell (d) 19.1%
SELECT "Incumbent" FROM table_18251 WHERE "Candidates" = 'Tom Ridge (R) 80.9% Joylyn Blackwell (D) 19.1%'
SELECT "Incumbent" FROM "table_18251" WHERE "Candidates" = 'Tom Ridge (R) 80.9% Joylyn Blackwell (D) 19.1%'