Cardinality and Power set?

These are some confusing questions I came across. What are the answers and is there any rule that can be used when there are nested sets as shown below?

What is the power set of {{},{{}}}?
What is the cardinality of {a,{a}}?
What is the cardinality of {{a}}?
What is the cardinality of {a,{a},{a,{a}}}?
3 คำตอบ 3