A candle burns a certain length per minute. After 8 minutes of ignition, the length of the candle is 12 cm. After 18 minutes, the length of the candle is 7 cm. What is the original length of the candle in cm?
蜡烛每分钟燃烧掉的长度一定，点火8分钟后，蜡烛的长度是12厘米，18分钟后长度是7厘米，蜡烛原来的长度是多少厘米．
<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>