My guess is that what the question designer meant is:
1(a) Suppose the student does the first essay question and the second essay question and the first MC question and then designates the MC question as bonus. This is not counted in 6*4*8.
1(b) We'd just use the original 6*4*8 and then add on the possibility that there is a sole MC bonus question, and that there is a sole essay bonus question, as such:
6*4*8 + C(6,2)*4 + C(4,2)*6