We know that it's 1 centimeter cubed per second. We know that this right over here is 1 centimeter cubed per second. We know what our height is right at this moment. We were told it is 2 centimeters. Our height right over here, we know it is 2 centimeters. So the only unknown we have over here is a rate at which our height is changing with respect to time, which is exactly what we needed to figure out in the first place. So we just have to solve for that.