There is a barrel of oil. After using up (2/3) of this barrel of oil, there is still 30 kilograms left. How many kilograms is this barrel of oil originally?
有一桶油，用去这桶油的(2/3)后，还剩30千克，求这桶油原来有多少千克？
<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">1 - (2/3)</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">30 / (1/3)</gadget>
<output>90</output>

<result>90</result>