As usual, also follow the general grading guidelines.

1.  1 pt #1
    1.5 pt #2
    2 pts #3 -- 1 pt each occurs1, occurs2
                occurs2 should use occurs1
    2.5 pts #4 -- -1 pt if recomputes a lot, should use local or helper 
function
                  may use scheme's build-in max

2.  3 pts total
    -.5 pt if forgets to finish third example

ec.  3 pts total
     1 pt first version
     1 pt second version
     1 pt simplifications
          first version can combine both cases where search-string empty
          second version can't combine those cases -- need a statement why