The outer diameter of a ring is 14 cm and the inner radius is 5 cm. What is the area of the ring in square centimeters?
一个环形外圆直径是14厘米，内圆半径是5厘米，这个环形的面积是多少平方厘米．
<gadget id="calculator">14 / 2</gadget>
<output>7</output>

<gadget id="calculator">7 ** 2</gadget>
<output>49</output>

<gadget id="calculator">5 ** 2</gadget>
<output>25</output>

<gadget id="calculator">49 - 25</gadget>
<output>24</output>

<gadget id="calculator">3.14 * 24</gadget>
<output>75.36</output>

<result>75.36</result>