So radius growing at rate of 1 centimeter per second. So given this, right now our circle, our ripple circle, has a radius of 3 centimeters. And we know that the radius is growing at 1 centimeter per second. Given that, at what rate is the area of circle growing? Area of circle growing. Interesting. So let's think about what we know and then what we don't know, what we're trying to figure out.