List the name of artists who have released albums and mixtape from 1980 to 1985 in "dance" genre.
albums and mixtape refer to releaseType; from 1980 to 1985 refers to groupYear between 1980 and 1985; tag = 'dance';
SELECT COUNT(T1.artist) FROM torrents AS T1 INNER JOIN tags AS T2 ON T1.id = T2.id WHERE T2.tag = 'dance' AND T1.groupYear BETWEEN 1980 AND 1985 AND T1.releaseType LIKE 'album' OR T1.releaseType LIKE 'mixtape'