The set S has 36 different subsets each of which contains exactly two elements. How many subsets of S could contain exactly three elements each?	Options:	A) 24	B) 42	C) 54	D) 72	E) 84
nC2 = 36   =&gt; n*(n-1)/2 = 36   =&gt; n = 9   nC3 = 9C3 = 84   So, Answer is 84.
<result>E</result>
The set S has 36 different subsets each of which contains exactly two elements. How many subsets of S could contain exactly three elements each?