There are 324 parts, Master Zhang produces 18 per day, and Master Li produces 15 per day. After 8 days of production by Master Zhang, Master Li continued to produce. How many days will it take Master Li to complete the task?
有324个零件，张师傅每天生产18个，李师傅每天生产15个．张师傅生产8天后由李师傅接着生产．李师傅还要多少天才能完成任务？
<gadget id="calculator">18 * 8</gadget>
<output>144</output>

<gadget id="calculator">324 - 144</gadget>
<output>180</output>

<gadget id="calculator">180 / 15</gadget>
<output>12</output>

<result>12</result>