A pile of sand is removed for the first time (4/7) and the second time (1/9). The second time is 10 tons less than the first time. How many tons is this pile of sand? What is the correct column
一堆沙子，第一次运走(4/7)，第二次运走(1/9)，第二次比第一次少运10吨，这堆沙子有多少吨？正确的列式为多少
<gadget id="calculator">4 / 7</gadget>
<output>4/7 = around 0.571429</output>

<gadget id="calculator">1 / 9</gadget>
<output>1/9 = around 0.111111</output>

<gadget id="calculator">(4/7) - (1/9)</gadget>
<output>29/63 = around 0.460317</output>

<gadget id="calculator">10 / (29/63)</gadget>
<output>630/29 = around 21.724138</output>

<result>630/29 = around 21.724138</result>