The length of the lower base of an isosceles trapezoid is 18cm, the length of the upper base is half of the length of the lower base, and the length of the waist is 12cm. What is the perimeter of this isosceles trapezoid?
一个等腰梯形的下底长18cm，上底长是下底的一半，腰的长为12cm，这个等腰梯形的周长是多少？
<gadget id="calculator">18 / 2</gadget>
<output>9</output>

<gadget id="calculator">12 * 2</gadget>
<output>24</output>

<gadget id="calculator">9 + 18 + 24</gadget>
<output>51</output>

<result>51</result>