A rectangular vegetable garden is 12 meters long and 3 meters wide. It is necessary to surround the vegetable garden with a fence. How long should the fence be?
一块长方形的菜园，长是12米，宽是3米，要在菜园的周围围上篱笆，请问要围多长的篱笆？
<gadget id="calculator">12 + 3</gadget>
<output>15</output>

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

<result>30</result>