The ratio of a pile of sand removed to the rest is 3:4. If 50 tons are removed, only 3/7 of this pile of sand is left. How many tons is this pile of sand originally?
一堆砂运走的和剩下的比是3：4，如果再运走50吨后，就剩下这堆砂的(3/7)，这堆砂原来有多少吨？
<gadget id="calculator">7 - 3</gadget>
<output>4</output>

<gadget id="calculator">4 / 7</gadget>
<output>4/7 = around 0.571429</output>

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

<gadget id="calculator">3 / 7</gadget>
<output>3/7 = around 0.428571</output>

<gadget id="calculator">(4/7) - (3/7)</gadget>
<output>1/7 = around 0.142857</output>

<gadget id="calculator">50 / (1/7)</gadget>
<output>350</output>

<result>350</result>