.
This question can be re-formulated in this way:
If you have a set of 4 elements, how many subsets does it have ?
The answer is: = 16 subsets, including the empty set and the improper set.
Re-phrasing back to your case and to your problem, there are 16 options, including the "empty" option.
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For many other similar problems see the lesson
- How many subsets are there in a given finite set of n elements?
in this site.
Also, you have this free of charge online textbook in ALGEBRA-II in this site
ALGEBRA-II - YOUR ONLINE TEXTBOOK.
The referred lesson is the part of this online textbook under the topic "Miscellaneous word problems".