CREATE TABLE table_2668336_24 (incumbent VARCHAR, candidates VARCHAR)

How many times is the candidates charles f. mercer (f) 100%?
SELECT COUNT(incumbent) FROM table_2668336_24 WHERE candidates = "Charles F. Mercer (F) 100%"
SELECT COUNT("incumbent") FROM "table_2668336_24" WHERE "Charles F. Mercer (F) 100%" = "candidates"