There is a batch of cement in the warehouse. After using this batch of cement (4/7), another 840 tons are transported in. At this time, the ratio of the cement in the warehouse to the original is 9:7. How many tons of cement are there in the warehouse at this time?
仓库里有一批水泥，用去这批水泥的(4/7)，又运进840吨，这时仓库里的水泥与原来的比是9：7，这时仓库有水泥多少吨？
<gadget id="calculator">9 / 7</gadget>
<output>9/7 = around 1.285714</output>

<gadget id="calculator">5 / 7</gadget>
<output>5/7 = around 0.714286</output>

<gadget id="calculator">(9/7) - (5/7)</gadget>
<output>4/7 = around 0.571429</output>

<gadget id="calculator">840 / (4/7)</gadget>
<output>1_470</output>

<gadget id="calculator">1_470 * (9/7)</gadget>
<output>1_890</output>

<result>1_890</result>