How many movies for mature audiences or parental guidance suggested did Bill Thompson work as a voice actor?
movies for mature audiences or parental guidance refer to movie_title where MPAA_rating = 'PG';
SELECT COUNT(T.movie) FROM ( SELECT T1.movie FROM `voice-actors` AS T1 INNER JOIN movies_total_gross AS T2 ON T1.movie = T2.movie_title WHERE MPAA_rating = 'PG' AND `voice-actor` = 'Bill Thompson' GROUP BY T1.movie ) AS T