1. Group songs into decades. Your result should record in such a format: Decade, songs.id, songs.title, songs.price. For example:

1970 5 Time 200

1970 4 Stairway to Heaven 510

1980 16 Billie Jean 1200

And so on for all the songs.

For songs from one decade, sort them, starting from the most expensive.

2. Change your query to not include albums with the undefined decade.