The radius of a circular coaster is 4 cm, what is the area of the coaster in square centimeters?
一个圆形杯垫的半径是4cm，这个杯垫的面积是多少平方厘米？
<gadget id="calculator">4 ** 2</gadget>
<output>16</output>

<gadget id="calculator">3.14 * 16</gadget>
<output>50.24</output>

<result>50.24</result>