What is the perimeter of a rectangle with a length of 12 cm and a width of 3 cm?
长12厘米，宽为3厘米的长方形，周长是多少厘米．
<gadget id="calculator">12 + 3</gadget>
<output>15</output>

<gadget id="calculator">15 * 2</gadget>
<output>30</output>

<result>30</result>