In general, follow the overall course grading guidelines.

#1.  1 pt for correct numbers
     .5 pts for correct singular/plural
     .5 pts for correct list form

     Better to use a helper function for singular/plural.

#2.  Should be a simple recursive function.
     Better to use a helper function for determining if something is expensive.

#3.  Should be a simple recursive function.

     -1 pt if returns only part of the appropriate pair.

#4.  -2 pts if doesn't have three cases.
     -.5 pts if ask (cons? (rest a-mnm)) in last two cases.
     -1 pt if select 2 items instead of 3 in last two cases.
     -1 pt if don't identify recursion.
     Optional in last two cases to use (and (cons? a-mnm) ...).

EC.  Should be a simple recursive function.
     Better to use a helper function for raising a single price.