So that's what our definite integral does. We go from y is equal to e to y is equal to e to the third power. So all we did, we're used to seeing things like this, where this would be 15 over x dx. All we're doing here is, this is 15 over y dy. So let's evaluate this. So we take the antiderivative of 15 over y, and then evaluate at these two points. So this is going to be equal to, antiderivative of one over y is going to be the natural log of the absolute value of y.