# Saw this somewhere

If a set $$X$$ contains $$n$$ elements. $$A$$ and $$B$$ are subsets of $$X$$. What is the probability that union of $$A$$ and $$B$$ is $$X$$? If the answer is $$k^n$$, find $$k$$.

Note: $$A$$ and $$B$$ can be equal.

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