A barrel of oil weighs (21/2) kilograms. After half of it is used, the weight of the barrels is (11/2) kilograms. If the price of oil is 8 yuan per kilogram, how much is the total value of this barrel of oil?
一桶油连桶重(21/2)千克，用去一半后，连桶重(11/2)千克，如每千克油卖8元，这桶油共值多少元？
<gadget id="calculator">21 / 2</gadget>
<output>21/2 = around 10.5</output>

<gadget id="calculator">11 / 2</gadget>
<output>11/2 = around 5.5</output>

<gadget id="calculator">(21/2) - (11/2)</gadget>
<output>5</output>

<gadget id="calculator">2 * 5 * 8</gadget>
<output>80</output>

<result>80</result>