40% of a barrel of oil is used up, and there are 84 kilograms left. How many kilograms is this barrel of oil originally?
一桶油用去40%，还剩84千克，这桶油原来有多少千克？
<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (2/5)</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">84 / (3/5)</gadget>
<output>140</output>

<result>140</result>