The upper base of an isosceles trapezoid is 6 cm, the lower base is twice as long as the upper base, and the waist is equal to the upper base. What is the perimeter of this isosceles trapezoid?
一个等腰梯形上底是6厘米，下底是上底的两倍，腰和上底相等．这个等腰梯形的周长是多少？
<gadget id="calculator">6 * 2</gadget>
<output>12</output>

<gadget id="calculator">6 + 12 + 6 + 6</gadget>
<output>30</output>

<result>30</result>