[plt-scheme] HTDP Exercises and language levels

Hi,

how do I find out which language level is supposed to be sufficient for 
a current exercise?

For instance:

I'm trying to solve an exercise in Section 6.6 HTDP and I think I know 
how to formulate the solution under an advanced language level, but I 
have the feeling, as this would require recursion and / or other things 
that have not yet been formally introduced yet, that this is not what 
the authors had in mind.

I've read through the previous over and over but couldn't find a hint 
which would give away the language level.

Best regards

Guenther