A batch of parts, if processing 30 parts per hour, can be completed 10 hours earlier than the original plan, if processing 20 parts per hour, can be completed 6 hours earlier than the original plan, how many parts are there in this batch?
一批零件，如果每时加工30个，可以比原计划提前10时完成，如果每时加工20个，可以比原计划提前6时完成，这批零件有多少个？
<gadget id="calculator">30 * 10</gadget>
<output>300</output>

<gadget id="calculator">20 * 6</gadget>
<output>120</output>

<gadget id="calculator">300 - 120</gadget>
<output>180</output>

<gadget id="calculator">30 - 20</gadget>
<output>10</output>

<gadget id="calculator">180 / 10</gadget>
<output>18</output>

<gadget id="calculator">18 - 6</gadget>
<output>12</output>

<gadget id="calculator">20 * 12</gadget>
<output>240</output>

<result>240</result>