For a batch of goods, 40% of the goods were transported for the first time, and 15 tons were transported for the second time. A total of 70% of the goods were transported for the two times. How many tons of the goods were there?
一批货物，第一次运走40%，第二次运走15吨，两次一共运走这批货物的70%，这批货物原来有多少吨？
<gadget id="calculator">70 / 100</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">40 / 100</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">15 / (3/10)</gadget>
<output>50</output>

<result>50</result>