An isosceles triangle has a perimeter of 20 meters and a waist of 8 meters. How long is the base of the triangle?
一个等腰三角形周长20米，腰长是8米，这个三角形底边长多少米？
<gadget id="calculator">8 * 2</gadget>
<output>16</output>

<gadget id="calculator">20 - 16</gadget>
<output>4</output>

<result>4</result>