​Find n{P(P(P(∅)))}

i did not understand can you explain me more clearly

The power set of any set has 2ⁿ elements where n denotes the no. of elements in the set..
So set phi is the empty set and it has no elements.
Therefore the no. of elements in P(phi) is 2⁰ since set phi has no elements.So the power set will have 1 element.
n(P(phi))=2⁰=1
n(P(P(phi))=2¹=2
n(P(P(P(phi))))=2²=4 elements.
Hope this will clear your doubts.