Additional question: The candle burns at a certain length per minute. A candle is 12 cm long after being ignited for 8 minutes, and 7 cm long after 18 minutes of igniting. What is the initial length of this candle in cm?
附加题：蜡烛每分钟燃烧的长度一定，一支蜡烛点火8分钟后长12厘米，点火18分钟后长7厘米，这支蜡烛最初的长度是多少厘米？
<gadget id="calculator">12 - 7</gadget>
<output>5</output>

<gadget id="calculator">18 - 8</gadget>
<output>10</output>

<gadget id="calculator">5 / 10</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(1/2) * 8</gadget>
<output>4</output>

<gadget id="calculator">4 + 12</gadget>
<output>16</output>

<result>16</result>