An umbrella factory rushed to manufacture a batch of tents to support the earthquake resistance in Yushu, Qinghai. On the first day, it produced 20% of the total number of tents, and on the second day it produced 7/20 of the total number of tents, leaving 3600 tents unfinished. How many tents are there in total?
某伞厂为支援青海玉树抗震赶制一批帐篷，第一天生产了总帐篷数的20%，第二天生产了总帐篷数的(7/20)，还剩3600顶帐篷没有完成．这批帐篷一共有多少顶？
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">7 / 20</gadget>
<output>7/20 = around 0.35</output>

<gadget id="calculator">1 - (1/5) - (7/20)</gadget>
<output>9/20 = around 0.45</output>

<gadget id="calculator">3_600 / (9/20)</gadget>
<output>8_000</output>

<result>8_000</result>