Zhang Jun processes a batch of parts. If he processes 30 parts per hour, he can complete the processing in 20 hours. If he processes 10 more parts per hour, how many hours can he complete the task?
张军加工一批零件，如果每小时加工30个，20小时可以加工完，如果每小时多加工10个，多少小时可以完成任务？
<gadget id="calculator">30 + 10</gadget>
<output>40</output>

<gadget id="calculator">20 / 40</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">30 * (1/2)</gadget>
<output>15</output>

<result>15</result>