The outer radius of a circle is 6cm, and the inner circumference is 15.7cm. What is the area of this circle in square centimetres?
一个圆环的外围半径是6cm，内圆的周长是15.7cm．这个圆环的面积是多少平方厘米？
<gadget id="calculator">6 ** 2</gadget>
<output>36</output>

<gadget id="calculator">15.7 / 3.14 / 2</gadget>
<output>2.5</output>

<gadget id="calculator">2.5 ** 2</gadget>
<output>6.25</output>

<gadget id="calculator">36 - 6.25</gadget>
<output>29.75</output>

<gadget id="calculator">3.14 * 29.75</gadget>
<output>93.415</output>

<result>93.415</result>