The waist of an isosceles triangle is twice the length of the base. The perimeter of the triangle is 40 cm. What is the length of the waist in cm?
等腰三角形的腰是底边长的2倍，三角形的周长是40厘米，腰长是多少厘米？
<gadget id="calculator">2 + 2 + 1</gadget>
<output>5</output>

<gadget id="calculator">40 / 5</gadget>
<output>8</output>

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

<result>16</result>