When transporting a batch of goods, the ratio of the transported goods to the remaining goods is 3:7. If another 30 tons are transported, the remaining goods will only account for (2/5) of the original goods. How many tons are the original goods?
运一批货物，运走的与剩下的比为3：7，如果再运走30吨，那么剩下的货物只占原有货物的(2/5)，这批货物原有多少吨？
<gadget id="calculator">3 + 7</gadget>
<output>10</output>

<gadget id="calculator">7 / 10</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(7/10) - (2/5)</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">30 / (3/10)</gadget>
<output>100</output>

<result>100</result>