A car factory planned to produce 18,000 cars last year, but completed (4/9) of the annual plan in the first half of the year, and (3/5) of the annual plan in the second half of the year. How many cars were actually over-produced?
某汽车厂去年计划生产汽车18000辆，结果上半年完成全年计划的(4/9)，下半年完成全年计划的(3/5)，实际超产了多少辆？
<gadget id="calculator">4 / 9</gadget>
<output>4/9 = around 0.444444</output>

<gadget id="calculator">3 / 5</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">(3/5) - 1</gadget>
<output>-2/5 = around -0.4</output>

<gadget id="calculator">(4/9) + (-2/5)</gadget>
<output>2/45 = around 0.044444</output>

<gadget id="calculator">18_000 * (2/45)</gadget>
<output>800</output>

<result>800</result>