Let's evaluate the expression $14 - 4x$ for both cases:

a) When $x = 9$:

Substitute $x = 9$ into the expression:

$14 - 4(9) = 14 - 36 = -22$

So, the value of $14 - 4x$ when $x = 9$ is $-22$.

b) When $x = -9$:

Substitute $x = -9$ into the expression:

$14 - 4(-9) = 14 + 36 = 50$

So, the value of $14 - 4x$ when $x = -9$ is 50.

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Let me know if you'd like more explanation or if you have any other questions! Here's a few related questions:

1. How would the expression change if we had $14 + 4x$ instead of $14 - 4x$?
2. What would happen if the expression involved a division by $x$?
3. Can you simplify the expression $14 - 4x$ further if $x$ is any number?
4. How do you graph the expression $14 - 4x$ as a straight line?
5. What would the expression look like if $x$ were replaced with $2x$?

Tip: Always double-check that the value you're substituting for $x$ is correctly placed into the expression to avoid errors during evaluation!