From part a I've established there are 14 combinations of picking the 4 items: {a,a,a,a} {a,a,a,s} {a,a,a,c} {a,a,s,s} {a,a,s,c} {a,a,c,c} {a,s,s,s} {a,s,s,c} {a,s,c,c} {a,c,c,c} {s,s,s,c} {s,s,c,c} {s,c,c,c} {c,c,c,c}
Assuming parts b and c are still talking about selecting 4 items, 4 of the...