A pile of sand has removed (2/7) of the total tonnage, and the rest is 2.1 tons more than what was removed. How many tons is this pile of sand?
一堆沙运走了总吨数的(2/7)，剩下的比运走的多2.1吨，这堆沙有多少吨？
<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">1 - (2/7) - (2/7)</gadget>
<output>3/7 = around 0.428571</output>

<gadget id="calculator">2.1 / (3/7)</gadget>
<output>4.9</output>

<result>4.9</result>