Xiao Ming tied a ox to a stake on the flat grass with a 5-meter-long rope. How much grass can the ox eat at the maximum?
小明把一头黄牛用5米长的绳子栓在平坦草地上的木桩上，那头黄牛最大限度能吃到多大面积的草呢？
<gadget id="calculator">5 ** 2</gadget>
<output>25</output>

<gadget id="calculator">3.14 * 25</gadget>
<output>78.5</output>

<result>78.5</result>