Me with this ! i need to turn it in today

use the following information:

u = {x | x is a natural number less than 20}

a = {x | x is an odd natural number less than 16}

b = {x | x is a prime number greater than 5}

(note: the prime numbers less than 20 are 2, 3, 5, 7, 11, 13, 17, and 19.) find the cardinality of each set.