Use a rope to measure the circumference of the tree. If it is wrapped twice around the tree, there will be 11 meters left. If it is wrapped four times, the difference will be 5 meters. Find the circumference of the tree in meters.
用一根绳子测量树的周长，如果绕树两圈，则余11米，如果绕树四圈，则差5米，求树的周长是多少米．
<gadget id="calculator">11 + 5</gadget>
<output>16</output>

<gadget id="calculator">4 - 2</gadget>
<output>2</output>

<gadget id="calculator">16 / 2</gadget>
<output>8</output>

<result>8</result>