Question 411808
For some subset within B,


10 may or may not be in the subset (2 choices)
12 may or may not be in the subset (2 choices)
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24 may or may not be in the subset. There are eight elements in B, and two choices for each element, so {{{2^8}}} possible subsets (just think of it as a burger place offering eight different condiments, how many ways to create a burger).