What im trying to do is make the bullet rotate to the same as the airplane.
You are not getting a reference to the bullet you are creating, to change its rotation. So, the compiler is taking 'bullet' as a class name and not as anything to do with the bullet object (obviously you cannot rotate a class). Do this:
// instead of
getWorld().addObject(new bullet(), getX(), getY());
// use this
bullet b = new bullet();
getWorld().addObject(b, getX(), getY());
Then, set the rotation of the bullet 'b' -- the reference to the bullet object.