The Third Machine Tool Factory produced a batch of lathes. It was originally planned to produce 30 lathes per day, but it could be completed within the scheduled time. The actual production was 36 per day, but it was completed 4 days ahead of schedule. How many lathes are there in this batch?
第三机床厂生产一批车床，原计划每天生产30台，可以在预定时间内完成，实际每天生产36台，结果提前4天完成了，这批车床共有多少台？
<gadget id="calculator">1 / 30</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">1 / 36</gadget>
<output>1/36 = around 0.027778</output>

<gadget id="calculator">(1/30) - (1/36)</gadget>
<output>1/180 = around 0.005556</output>

<gadget id="calculator">4 / (1/180)</gadget>
<output>720</output>

<result>720</result>