Answer: 64
Step-by-step explanation
Imagine we had 6 light switches. They represent 'a' through 'f'.
Light switch number 1 being flipped on means we include 'a', and it turned off means we exclude 'a'. The same idea applies to the other switches.
Each switch has 2 choices, so there are (2*2*2)*(2*2*2) = 2^6 = 64 different combos of on/off. That's the number of subsets of {a,b,c,d,e,f}.
The general rule is that if we had n elements in the set, then there are 2^n different subsets. This includes the set itself and the empty set.
Note: The power set is the set of all subsets of a given set.