This is our outer radius, which is also going to be equal to that right over there. So that's the distance between y equals 4 and the function that's defining our outside. The distance between y equals 4 and the function that is defining our outside. So this is essentially, this height right over here is going to be equal to 4 minus x squared minus 2x. I'm just finding the distance, or the height, between these two functions. So the outer radius is going to be 4 minus this. Minus x squared minus 2x, which is just 4 minus x squared plus 2x.