The perimeter of an isosceles triangle is 42 cm, the base is 12 cm, and the waist is in cm.
一个等腰三角形的周长是42厘米，底长12厘米，腰长多少厘米．
<gadget id="calculator">42 - 12</gadget>
<output>30</output>

<gadget id="calculator">30 / 2</gadget>
<output>15</output>

<result>15</result>