A = {a, b, c, d} How many subsets does the set A have?

A has:
1 subset with zero elements = ∅
4 subsets with one element = {a}, {b}, {c} and {d}
6 subsets with two elements = {a, b}, {a, c}, {a, d}, {b, c}, {b, d} and {c, d}
4 subsets with three elements = {a, b, c}, {a, b, d}, {a, c, d} and {b, c, d}
1 subset with four elements = {a, b, c, d}
Therefore A has 16 subsets altogether.
Note:
1. Remember that order doesn't matter. So, for example, {a, b} and {b, a} are the same subset.
2. The numbers 1, 4, 6, 4 and 1 are Binomial coefficients and occur in the fifth row of Pascal's triangle.
3. 16 = 24. Generally a set with n elements has 2n subsets.
I found an answer from www.quora.com
If A= {a, b,c, d}, then how many subsets does the set A have? - Quora
The number of subsets of a set is 2^n, where n is the cardinality of the set. D has 4 elements. So it has 2^4 = 16 subsets, including The Empty Set and D itself.
For more information, see If A= {a, b,c, d}, then how many subsets does the set A have? - Quora
I found an answer from en.wikipedia.org
Power set - Wikipedia
In mathematics, the power set (or powerset) of a set S is the set of all subsets of S , including the ... For example, the power set of a set with three elements, has: ... the singleton subsets),; C(3, 3) = 1 subset with 3 elements (the original set itself). ... However, there are two important properties of subsets that do not carry over to ...
For more information, see Power set - Wikipedia