How many times was the candidates paul tsongas (d) 60.6% paul w. cronin (r) 39.4%?
create table table_1341690_21 (incumbent varchar, candidates varchar, PRIMARY KEY (incumbent))
select count(incumbent) from table_1341690_21 where candidates = "paul tsongas (d) 60.6% paul w. cronin (r) 39.4%"