The radius of the bottom surface of a wooden barrel is 40 cm. Now use thick iron wire to surround the side of the barrel for 3 circles. How many meters of thick iron wire are needed at least?
一个木桶的底面半径是40厘米，现用粗铁丝在木桶侧面围上了3圈，至少需要多少米的粗铁丝？
<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">3.14 * (2/5) * 2 * 3</gadget>
<output>7.536</output>

<result>7.536</result>