That's the inner function, at least over the interval that we care about. So the area of this washer, we could just leave it like this, or we could factor out a pi. We could say it's equal to the area is equal to, if we factor out a pi, pi times f of x squared, f of x squared minus g of x squared. Minus, I don't, I have to write a parentheses there. So we could write f of x squared minus g of x squared. And then if we want the volume, put that in that same yellow. If we want the volume of this thing, we just multiply it times the depth of each of those washers.