A cow is tied to a tree stump to graze. The rope is 5 meters long. How much grass can the cow eat?
一头牛栓在树桩上吃草，绳长5米，这头牛能吃到多大面积的草？
<gadget id="calculator">5 ** 2</gadget>
<output>25</output>

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

<result>78.5</result>