SOLUTION
Giving The set

Then from cartesian coordinate of a set,

Then we expand the set above

The extension of a set is the set itself.
Hence

Extension A² = {(p,p),(p,q),(p,r),(q,p),(q,q),(q,r),(r,p),(r,q),(r,r)}
The cardinality of a set is the number of elements in the set.

Hence
Card A²=9
Then Card A is

Therefore

Therefore
cardA²=(card)²=9