After adding 20% of a number, it is 8.4. Find this number.
一个数加上它的20%后是8.4，求这个数．
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 + (1/5)</gadget>
<output>6/5 = around 1.2</output>

<gadget id="calculator">8.4 / (6/5)</gadget>
<output>7</output>

<result>7</result>