There is a pile of coal in a canteen. After using (3/5), another 840 kilograms is brought in. At this time, the coal is 10% more than before. How many kilograms of coal are there originally?
某食堂有一堆煤，用去(3/5)后，又运来840千克，这时的煤比原来多10%，原来有煤多少千克？
<gadget id="calculator">10 / 100</gadget>
<output>1/10 = around 0.1</output>

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

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

<gadget id="calculator">(1/10) - (2/5)</gadget>
<output>-3/10 = around -0.3</output>

<gadget id="calculator">1 + (-3/10)</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">840 / (7/10)</gadget>
<output>1_200</output>

<result>1_200</result>