Use 28 cm long iron wire to form an isosceles triangle. If the length ratio of the waist to the base is 3:1, what is the length of the waist in centimeters?
用28厘米长的铁丝围成一个等腰三角形，已知腰和底的长度比是3：1，则腰长多少厘米．
<gadget id="calculator">3 + 3 + 1</gadget>
<output>7</output>

<gadget id="calculator">3 / 7</gadget>
<output>3/7 = around 0.428571</output>

<gadget id="calculator">28 * (3/7)</gadget>
<output>12</output>

<result>12</result>