The expression in the image is:
$x = z - y$

This is a simple linear equation relating the variables $x$, $y$, and $z$. It states that $x$ is equal to the difference between $z$ and $y$.

Would you like to see a step-by-step solution or have any further questions related to this?

Here are some related questions for exploration:

1. How can we solve for one variable if we know the values of the other two?
2. What is the graphical representation of this equation?
3. How do we solve systems of equations that involve such linear relationships?
4. How do we apply this equation in practical real-life problems?
5. What happens if we rearrange this equation to isolate $y$ or $z$?

Tip: When working with equations like this, always try to isolate the variable you're solving for by performing inverse operations!