The upper base of an isosceles trapezoid is 3 cm, the lower base is 5 cm, and its perimeter is 20 cm. What is the waist of this isosceles trapezoid?
一个等腰梯形的上底是3厘米，下底是5厘米，它的周长是20厘米．这个等腰梯形的腰是多少厘米？
<gadget id="calculator">20 - 3 - 5</gadget>
<output>12</output>

<gadget id="calculator">12 / 2</gadget>
<output>6</output>

<result>6</result>