A construction company in Luoyang plans to install another batch of prefabricated houses for the earthquake-stricken areas in Sichuan in July. They completed the planned (1/2) in the first ten days, (3/7) in the middle ten days, and 450 units in the second ten days, and the result exceeded the plan. (1/4), how many sets of prefabricated houses did the construction company plan to install?
洛阳市一建筑工司七月份计划为四川地震灾区再安装一批活动板房，他们上旬完成计划的(1/2)，中旬完成了(3/7)，下旬完成了450套，结果超过计划的(1/4)，建筑公司原计划安装活动板房多少套？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">3 / 7</gadget>
<output>3/7 = around 0.428571</output>

<gadget id="calculator">1 - (1/2) - (3/7)</gadget>
<output>1/14 = around 0.071429</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(1/14) + (1/4)</gadget>
<output>9/28 = around 0.321429</output>

<gadget id="calculator">450 / (9/28)</gadget>
<output>1_400</output>

<result>1_400</result>