A barrel of oil, when 25% is used, weighs 10.5 kg; when 45% is used, the weight of the barrel is 8 kg. How many kilograms does the barrel weigh?
一桶油，用去25%后，连桶重10.5千克；当用去45%后，连桶重8千克．桶重多少千克？
<gadget id="calculator">10.5 - 8</gadget>
<output>2.5</output>

<gadget id="calculator">45 / 100</gadget>
<output>9/20 = around 0.45</output>

<gadget id="calculator">25 / 100</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(9/20) - (1/4)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">2.5 / (1/5)</gadget>
<output>12.5</output>

<gadget id="calculator">1 - (1/4)</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">12.5 * (3/4)</gadget>
<output>9.375</output>

<gadget id="calculator">10.5 - 9.375</gadget>
<output>1.125</output>

<result>1.125</result>