using not with sub-queries

Question

I have been asked to display results in my sql server database for the following question

What software packages are not installed on any HP computers?

Answer 1

;with installed as
( select PACK from software where TAGNUM in ( select tagnum from PC where comp in ( select comp from computer where MFRNAME = 'HP')))
select * from Package p left join installed i on p.pack = i.pack
where i.pack is null