The expression you provided is $9 \times x - y$, which can be written mathematically as:

$9x - y$

This expression represents 9 times a variable $x$, minus another variable $y$.

Would you like more details or have any other questions?

Here are five related questions:

1. What happens if $x = 2$ and $y = 5$? What is the value of the expression $9x - y$?
2. How would you solve the equation $9x - y = 0$ for $x$?
3. What is the effect of increasing $y$ on the value of the expression $9x - y$?
4. How would the expression change if it was $9x + y$ instead of $9x - y$?
5. Can you graph the equation $y = 9x - y$?

Tip: When dealing with expressions involving multiple variables, remember that each variable can represent a different value, and the expression's outcome depends on the values assigned to these variables.