That should be 2^n and not just 2n
If we have 4 subsets, then 2^n = 4 leads to n = 2 since 2^2 = 4.
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Here's an example.
A = {p,q}
The four subsets of set A = {p,q} are
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Here's an example with n = 3 elements. We'll have 2^n = 2^3 = 8 subsets now. Let's say we had B = {r,s,t}
Those 8 subsets of set B are...
Note that order does not matter within any given set. Something like {r,s} is the same as {s,r}.