A test field is 9 meters long and 6 meters wide, what is the circumference of the test field in meters?
一块试验田长9米，宽6米，这块试验田的周长是多少米？
<gadget id="calculator">9 + 6</gadget>
<output>15</output>

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

<result>30</result>