A rectangular vegetable field is 15 meters long and three times its width. What is the perimeter of this vegetable field in meters?
一块长方形菜地，长15米，是宽的3倍，这块菜地的周长是多少米？
<gadget id="calculator">15 / 3</gadget>
<output>5</output>

<gadget id="calculator">15 + 5</gadget>
<output>20</output>

<gadget id="calculator">20 * 2</gadget>
<output>40</output>

<result>40</result>