Answer
n(A) = 12
Work Step by Step
A = {X|X is a month of a year}
We know that months of the year are : January, February, March, April, may, June, July, August, September, October, November, December.
Therefore the Set A = {January, February, March, April, may, June, July, August, September, October, November, December}
So, there are 12 elements in the set = cardinal no = n(A) = 12.
