Closing a form from another one

Hi, using the netbeans Gui builder i made 2 form, "a" and "b"

If i need to close form "a" from "a" i simply need to use:

this.setVisible(false);

it works! :D

but now i need to close "a" from "b" :|

using a.setVisible(false); makes an "non-static method setVisible(boolean) cannot be referenced from
a static context" :(

How can i close "a" from "b"? :(

thank you :)