A barrel of oil, I ate (1/4) of the total in the first week, and (1/5) of the total in the second week, and I ate 4 kilograms less in the second week than in the first week. How many kilograms of this barrel of oil are there in total? ?
一桶油，第一周吃了总数的(1/4)，第二周吃了总数的(1/5)，第二周比第一周少吃了4千克，这桶油一共有多少千克？
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/4) - (1/5)</gadget>
<output>1/20 = around 0.05</output>

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

<result>80</result>