Use two wooden sticks with lengths of 30cm and 12cm respectively to form a rectangle. What is the perimeter of this rectangle in centimeters?
用长度分别是30cm和12cm的木条各两根，围成一个长方形．这个长方形的周长是多少厘米？
<gadget id="calculator">30 + 12</gadget>
<output>42</output>

<gadget id="calculator">42 * 2</gadget>
<output>84</output>

<result>84</result>