The school playground is an approximate rectangle with a length of 60 meters and a width of 40 meters. Green belts are planted around it. How long is the green belt at least?
学校操场是一个长60米，宽40米的近似的长方形，在它的四周栽上绿化带，绿化带长至少多少米？
<gadget id="calculator">60 + 40</gadget>
<output>100</output>

<gadget id="calculator">100 * 2</gadget>
<output>200</output>

<result>200</result>