And what we're curious about is what is the derivative with respect to x of h of x at x is equal to 9. And so I encourage you to pause this video and think about it on your own before I work through it. So let's think about it a little bit. So another way just to get familiar with the notation of writing this, the derivative of h of x with respect to x at x equals 9. This is equivalent to h. Let me do it in that blue color. It is equivalent to h prime. And the prime signifies that we're taking the derivative.