Zhang Ming is grazing sheep by tying a sheep to a stake. The length of the rope from the stake to the neck of the sheep is 4m. What is the area in square meters that the sheep can eat grass?
张明放羊是将一只羊拴在木桩上，木桩到羊颈的绳长是4m，这只羊能吃到草的面积是多少平方米．
<gadget id="calculator">4 ** 2</gadget>
<output>16</output>

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

<result>50.24</result>