A barrel is filled with half a barrel of oil, and there is 15 kilograms left after pouring out the oil (1/5). How many kilograms of oil can this barrel hold?
一只桶，装了半桶油，倒出油的(1/5)还剩15千克，这只桶能装油多少千克．
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (1/5)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">15 / (4/5)</gadget>
<output>75/4 = around 18.75</output>

<gadget id="calculator">(75/4) * 2</gadget>
<output>75/2 = around 37.5</output>

<result>75/2 = around 37.5</result>