[plt-scheme] Stuck with exercise examples in HTDP

Hi,

I'm trying to teach myself Scheme mit DrScheme and HTDP and now I'm 
stuck with a particular exercise in HTDP (6.6.6 - 
draw-and-clear-circle), I just don't have a clue. I'd know how to do it 
in Lisp though.

I would like to look up the solution but it seems I won't get access to 
the solutions without registering as a teacher which I'm not (other than 
teaching myself).

How is the book (HTDP) to be used for someone like me (self-teaching) 
without access to the solutions?

How do you guys go about this then in a similar situation?

Cheers Günther