If the base length of an isosceles triangle is 12 cm and the waist length is 15 cm, what is its perimeter in cm?
一个等腰三角形的底长是12厘米，腰长是15厘米，它的周长是多少厘米．
<gadget id="calculator">15 * 2</gadget>
<output>30</output>

<gadget id="calculator">12 + 30</gadget>
<output>42</output>

<result>42</result>