The perimeter of an isosceles triangle is 40 centimeters, and one of its sides is 12 centimeters long. How long is its base in centimeters?
等腰三角形的周长是40厘米，它的一条腰长12厘米，那么，它的底边长多少厘米？
<gadget id="calculator">12 * 2</gadget>
<output>24</output>

<gadget id="calculator">40 - 24</gadget>
<output>16</output>

<result>16</result>