Half of a barrel of gasoline is used up, and 20 kilograms are added. At this time, the gasoline in the barrel just accounts for 3/4 of the whole barrel. How many kilograms does this barrel of gasoline weigh?
一桶汽油用去一半，又加进20千克，这时桶里的汽油正好占全桶的(3/4)，这桶汽油重多少千克？
<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(3/4) - (1/2)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">20 / (1/4)</gadget>
<output>80</output>

<result>80</result>