And what you see in region S, the function f is greater than the function g. It's above the function g. And so we can write h of x. We could write h of x as being equal to f of x minus g of x. And what we want to do is we want to find the rate at which h changes with respect to x. And so we could write that as h prime of, we could say h prime of x, but we want the rate when x is equal to 1.8. So h prime of 1.8 is what we want to figure out. Now we could evaluate f prime of 1.8 and g prime of 1.8, and to do that we would take the derivatives of each of these things and we know how to do that. It's within our capabilities.