Use a 48 cm long iron wire to form an isosceles trapezoid. Measure the upper base to be 8 cm long and the lower base to be 20 cm long. Find its waist length.
用一根长48厘米的铁丝围成一个等腰梯形，量得上底长8厘米，下底长20厘米，求它的腰长．
<gadget id="calculator">48 - 8 - 20</gadget>
<output>20</output>

<gadget id="calculator">20 / 2</gadget>
<output>10</output>

<result>10</result>