This took me around 2 hours or a bit more. Within the first image, there are 11 thumbnail sketches choosing three out of them create one ambiguous figure and two stable. The second shows an ambiguous figure due to the lines reaching towards the edges of the page. Along with having an unstable ground as the white parts of the image can also be a fous point. The final two picture are stable as it shows clearly what the fous is along with having a larger bakground that supports that image.
My favorite one is the second one because I saw you adding a variety of thick lines to the cracks and it made it really pretty!