A pile of sand takes up 3 tons, which takes up exactly (3/7) of the pile of sand, how many tons are left? What is the column
一堆沙子，用去3吨，正好占这堆沙子的(3/7)，还剩多少吨？列式为多少
<gadget id="calculator">3 / 7</gadget>
<output>3/7 = around 0.428571</output>

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

<gadget id="calculator">7 - 3</gadget>
<output>4</output>

<result>4</result>