A barrel of oil weighs 12 kilograms, and after half of the oil is sold, the weight of the barrel is 6.75 kilograms. If the price per kilogram of oil is 4.2 yuan, how much is it sold for?
一桶油连桶重12千克，卖出油的一半后，连桶重6.75千克．如果每千克油的价格是4.2元，卖出多少元？
<gadget id="calculator">12 - 6.75</gadget>
<output>5.25</output>

<gadget id="calculator">4.2 * 5.25</gadget>
<output>22.05</output>

<result>22.05</result>