Even x is a function, must be a function of something else. Well, they tell us that the derivative of x with respect to t is 12. And they want us to find the derivative of y with respect to t when x is equal to nine. So let's just make sure we can understand this. So they're telling us that both x and y are functions. Arguably, they're both functions of t. Y is a function of x, but then x is a function of t, so y could also be a function of t. One way to think about it is if x is equal to f of t, then y is equal to the square root of x, which would just be f of t. Another way to think about it, if you took t as your input into your function f, you're going to produce x. And then if you took that as your input into the square root function, you are going to produce y.