1. The problem is to understand the difference between the number 2 and the variable $z$. 2. In mathematics, $2$ is a constant number, which means it always represents the same value. 3. The letter $z$ is a variable, which means it can represent any number or value depending on the context. 4. For example, if you have an equation $z + 3 = 5$, you can solve for $z$ by subtracting 3 from both sides: $$z + 3 = 5$$ $$z = 5 - 3$$ $$z = 2$$ 5. This shows that $z$ can take the value 2 in this case, but $z$ itself is not always 2; it depends on the equation or problem. 6. So, $2$ is a fixed number, while $z$ is a symbol that can represent different numbers.