The perimeter of an isosceles trapezoid is 30 cm, the upper and lower bases are 8 cm and 10 cm respectively, what is the length of each waist in cm?
一个等腰梯形的周长是30厘米，上底和下底分别为8厘米、10厘米，每条腰长多少厘米．
<gadget id="calculator">30 - 8 - 10</gadget>
<output>12</output>

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

<result>6</result>