Your post has several errors in it. There's no A until the final line of your post and your set X contains only elements such that X>=4 which doesn't make any sense.
I assume your intended question is
[tex]A= \{x\ :\ x\in \mathbb{N}\ &\ x\geq4 \}[/tex]
[tex]B=\{x\ :\ x\in \mathbb{N}\ &\ x<5 \}[/tex]
and you want to find [tex]A\cap B[/tex]
You have to show what work you've done so far. How have you tried to solve the problem?
Assuming, as Office Shredder suggests, that your sets are
[itex]A= \{n |n\in \mathbb{N} , \ n\ge 4\}[/itex]
and
[itex]B= \{n| n\in \mathbb{N} ,\ n< 5\}[/itex]
Can you list some members of A and b? What natural numbers are greater than or equal to 4? What natural numbers are less than 5?