You've got to use the combination area to combine materials into a new W key, first combine the big W and the scissors into a small W, then combine the small W with the white paint to make a white W, then combine the white W with an empty key box to make the new W key! When combining make sure not to stack the items on top of each other in the combination space, leave some space in between them. If they are too close the red X will appear.