For a barrel of oil, 40% is taken out for the first time, and 10 kg less is taken out for the second time than the first time, and there are 28 kg left in the barrel. How many kilograms of this barrel of oil are there?
一桶油，第一次取出40%，第二次比第一次少取出10千克，桶里还剩28千克，这桶油原有多少千克？
<gadget id="calculator">28 - 10</gadget>
<output>18</output>

<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (2/5) - (2/5)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">18 / (1/5)</gadget>
<output>90</output>

<result>90</result>