One could reasonably argue that beyond four sets of elements, Venn diagrams lose their utility. The four-ellipse image is already pretty chaotic. Maybe for five-plus sets we should abandon visual ...

In set notation this is B = {1, 4, 9}. 30 people answered a survey about whether they have a dog or a cat. The Venn diagram shows the information from the survey. 13 people have got a dog.