Xiao Ming used a 25cm long thin iron wire to surround an isosceles trapezoid with an upper base of 5 cm and a lower base of 8 cm. What is the length of one waist of this isosceles trapezoid in cm?
小明用一根25cm长的细铁丝围了一个上底是5cm，下底是8cm的等腰梯形，这个等腰梯形的一条腰长多少cm．
<gadget id="calculator">25 - 5 - 8</gadget>
<output>12</output>

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

<result>6</result>