After 75% of a barrel of oil is used up, there are still 12 kilograms in the barrel. How many kilograms of original oil is in the barrel?
一桶油用去75%后，桶内还有12千克．桶内原有油多少千克？
<gadget id="calculator">75 / 100</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">1 - (3/4)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">12 / (1/4)</gadget>
<output>48</output>

<result>48</result>