Before he leaves Pencey Prep, does Holden sells a typewriter?

He sells his ninety-dollar typewriter down the hall for twenty bucks.

Holden sells his typewriter yes because when an old person is about to die or feels like they are dying what do they do? They sell all their stuff to people. in that case Holden feels like he is about to die so he sold his typewriter even though he doesn't really need the money.