There was a batch of goods in a certain warehouse, and 840 tons of goods were shipped out (2/5). At this time, the total number of goods increased by 30% compared with the original one. How many tons of goods did the warehouse originally have?
某仓库原有一批货物，运出(2/5)后又运来840吨，这时货物总数比原来增加了30%，求仓库原来有货物多少吨？
<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (2/5)</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">(3/10) - (3/5)</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>