A wire encloses a square with an area of 100 square centimeters, which is changed to form an isosceles trapezoid with an upper base of 8 cm and a lower base of 18 cm. What is the length of its waist in cm?
一根铁丝围成一个面积为100平方厘米的正方形，改围成一个等腰梯形，上底是8厘米，下底是18厘米，它的腰长多少厘米．
<gadget id="calculator">10 * 4</gadget>
<output>40</output>

<gadget id="calculator">40 - 8 - 18</gadget>
<output>14</output>

<gadget id="calculator">14 / 2</gadget>
<output>7</output>

<result>7</result>