How many trucks are in both movies and musical playlists. | Did you mean to ask for the number of tracks in both movies and music playlists? | yes
SELECT COUNT ( * )  FROM  ( SELECT T1.name FROM tracks AS T1 JOIN playlist_tracks AS T2 ON T1.id  =  T2.track_id JOIN playlists AS T3 ON T2.playlist_id  =  T3.id WHERE T3.name  =  'Movies' INTERSECT SELECT T1.name FROM tracks AS T1 JOIN playlist_tracks AS T2 ON T1.id  =  T2.track_id JOIN playlists AS T3 ON T2.playlist_id  =  T3.id WHERE T3.name  =  'Music' ) 
number of tracks in both movies and music playlists refers to the intersection of tracks present in both 'Movies' and 'Music' playlists; count of tracks = COUNT(*);