A barrel of oil weighs 15 kilograms in total. After selling (3/4), the weight of the barrels is 6 kilograms. How many kilograms does this barrel of oil weigh? (calculated by equation)
一桶油连桶共重15千克，卖出(3/4)以后，连桶重6千克．这桶油重多少千克？(用方程计算)
<gadget id="calculator">15 - 6</gadget>
<output>9</output>

<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">9 / (3/4)</gadget>
<output>12</output>

<result>12</result>