Table schema:
CREATE TABLE table_1341690_21 (incumbent VARCHAR, candidates VARCHAR)

Question: How many times was the candidates paul tsongas (d) 60.6% paul w. cronin (r) 39.4%?
SQL: SELECT COUNT(incumbent) FROM table_1341690_21 WHERE candidates = "Paul Tsongas (D) 60.6% Paul W. Cronin (R) 39.4%"