A sheep is tied to the grass with a 3.1m long rope, and a 0.1m long rope is used to tie the sheep. How much m**2 grass can this sheep eat at most?
用一根3.1m长的绳子的把一只羊拴在草地上，拴羊时打结用了0.1m长的绳子．这只羊最多能吃到多少m**2的草？
<gadget id="calculator">3.1 - 0.1</gadget>
<output>3</output>

<gadget id="calculator">3 ** 2</gadget>
<output>9</output>

<gadget id="calculator">3.14 * 9</gadget>
<output>28.26</output>

<result>28.26</result>