If A={5x/x belongs to Z,x less than or equal to 30} B={x/x is a prime number;1 less than or equal to x less than or equal to 25}verify whether A and B are disjoint or intersecting sets.

Answer 1

well, just list the elements of A and B:
A = {...-15,-10,-5,0,5,10,15,...,150}
B = {2,3,5,7,11,13,17,19,23}
so, what do you think?

I suspect you really meant
A = {x|x ε N, x≤30}
since those are the positive integers