Conversation so far:
When did Dan Brown become a songwriter?
In 1991 Dan Brown moved to Hollywood to pursue a career as singer-songwriter and pianist.
What was Dan Brown's first published song?
After graduating from Amherst, Dan Brown dabbled with a musical career, creating effects with a synthesizer, and self-producing a children's cassette entitled SynthAnimals
Was Dan Brown's first cassette SynthAnimals successful?
Dan Brown sold a few hundred copies of SynthAninals.
What did Dan Brown write next after SynthAnimals?
Dan Brown then in 1990 self-published a CD entitled Perspective.
Was Dan Brown's second CD Perspective successful?
Dan Brown's Perspective CD also sold a few hundred copies
Did he release any more music after SynthAnimals and Perspective?
In 1994 Brown released a CD titled Angels & Demons.
Where did Dan Brown teach?
To support himself, Dan Brown taught classes at Beverly Hills Preparatory School.

Question: How long did he teach there?
Self-contained rewrite: How long did Dan Brown teach at Beverly Hills Preparatory School?