The sum of the upper and lower bases of an isosceles trapezoid is 30 cm and its waist is 10 cm. What is the perimeter of this trapezoid?
一个等腰梯形的上底与下底之和为30厘米，腰长为10厘米．这个梯形的周长是多少？
<gadget id="calculator">10 * 2</gadget>
<output>20</output>

<gadget id="calculator">30 + 20</gadget>
<output>50</output>

<result>50</result>