There is a barrel of oil, 1/4 of it is taken out for the first time, and 4 kg less than the first time is taken out for the second time, leaving 19 kg. How much does this barrel of oil weigh?
有一桶油，第一次取出它的(1/4)，第二次比第一次少取4千克，还剩下19千克，原来这桶油重多少千克？
<gadget id="calculator">19 - 4</gadget>
<output>15</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 - (1/4) - (1/4)</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">15 / (1/2)</gadget>
<output>30</output>

<result>30</result>