An air conditioner production workshop originally planned to produce 40 air conditioners per day, and the task could be completed in 15 days; the actual daily production was 10 more than the original plan. How many days did it actually take to produce this batch of air conditioners?
某空调生产车间，原计划每天生产40台空调，15天可以完成任务；实际每天比原计划多生产10台，实际生产这批空调用了多少天？
<gadget id="calculator">40 + 10</gadget>
<output>50</output>

<gadget id="calculator">15 / 50</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">40 * (3/10)</gadget>
<output>12</output>

<result>12</result>