It is really difficult to interpret what you have posted.
I take it that A is the set of multiples of 15 from 1 to .
B is the set of multiples of 33 from 1 to .
The question want to know how elements are in the set .
That is the number of integers from 1 to which are multiples of 15 and not multiples of 33.
That is .
If that is not what you mean, then what do you mean?