A basketball court is a rectangle with a length of 20 meters and a width of 10 meters. What is its perimeter in meters?
篮球场是一个长方形，长20米，宽10米，它的周长是多少米．
<gadget id="calculator">20 + 10</gadget>
<output>30</output>

<gadget id="calculator">30 * 2</gadget>
<output>60</output>

<result>60</result>