Xiaoming's family has a rectangular vegetable field, 12 meters long and 8 meters wide. The longer side of the vegetable field is against the wall, and the other three sides are surrounded by fences. How many meters of fences are needed?
小明家有一块长方形的菜地，长12米，宽8米，菜地较长的一面靠墙，其它三面用篱笆围上，需要篱笆多少米？
<gadget id="calculator">8 * 2</gadget>
<output>16</output>

<gadget id="calculator">12 + 16</gadget>
<output>28</output>

<result>28</result>