Master Wang processed a batch of parts, 20 per hour on the first day, and 30 per hour on the second day. The same amount was processed in the two days. It took 13.5 hours. How many parts are there in this batch?
王师傅加工一批零件，第一天每小时加工20个，第二天每小时加工30个，两天加工的数量同样多，共用了13.5小时，这批零件共有多少个？
<gadget id="calculator">405 / 50</gadget>
<output>81/10 = around 8.1</output>

<gadget id="calculator">20 * (81/10)</gadget>
<output>162</output>

<gadget id="calculator">13.5 - (81/10)</gadget>
<output>5.4</output>

<gadget id="calculator">30 * 5.4</gadget>
<output>162</output>

<gadget id="calculator">162 + 162</gadget>
<output>324</output>

<result>324</result>