Now, for left cosets we know , and we know that cosets all have equal size (they have size ). Thus, you need to find however many sets of 4 elements not in such that for all 4 elements.
These will be your left cosets. For your right cosets, you apply a similar formula ( ).
Remember that left and right cosets are equal if and only if your subgroup is . I'm afraid I can't tell you off hand whether is normal, although I am pretty positive it is. is definitely normal. So, hopefully, in each case your left and right cosets will be equal.