So we want to evaluate f prime, we want to figure out what f prime of, f prime of two is equal to. So we know that f prime of x, f prime of x, which is the same thing as dy, dx, is equal to two times x minus y. We saw that in the last problem. And so f prime of two, right this way, f prime of two is going to be equal to two times two, two times two, minus whatever y is when x is equal to two. Well, do we know what y is when x equals to two? Sure, they tell us right over here. Y is equal to f of x.