square of grass, with a side length of 6 meters, is tied to a vertex of the square with a rope of 4 meters, and a cow is let to graze on the grass. What is the maximum area of grass that the cow can eat?
一块正方形草地，边长6米，用一根长4米的绳子，在正方形的一个顶点上拴住一头牛，让牛到草地上吃草，牛最多能吃到多大面积的草？
<gadget id="calculator">4 ** 2</gadget>
<output>16</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">3.14 * 16 * (1/4)</gadget>
<output>12.56</output>

<result>12.56</result>