Use is a subset of or not a subset of to fill in the gap: The Venn diagram shows that 𝑍 blank 𝑋.
This sideways U is a symbol to tell us that something is a subset of something else. You could think of it as something being contained in something else. The other symbol the sideways U with the slash through it represents the statement it is not a subset of or it is not contained in.
In our statement, the Venn diagram shows that 𝑍 blank 𝑋. We have to answer the question, is 𝑍 a subset of 𝑋? Is 𝑍 contained in 𝑋? The subset 𝑍 is located in the red circle. But the entire red circle is inside the green square. And that tells us that everything in 𝑍 is contained in 𝑋. That makes 𝑍 a subset of 𝑋.
We can fill in the gap with the subset symbol: 𝑍 is a subset of 𝑋.