A cylindrical oil barrel is filled with half a barrel of oil. After pouring out 40% of the oil in the barrel, there are 21 liters left. It is known that the bottom area of the oil barrel is 560 square centimeters. How many decimeters is the height of the oil barrel?
一个圆柱形油桶，里面装了半桶油，把桶里的油倒出40%后，还剩21升，已知油桶的底面积是560平方厘米，油桶的高是多少分米？
<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (2/5)</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">21 / (3/5)</gadget>
<output>35</output>

<gadget id="calculator">1_000 / 560 / 10</gadget>
<output>5/28 = around 0.178571</output>

<gadget id="calculator">35 * 2 * (5/28)</gadget>
<output>25/2 = around 12.5</output>

<result>25/2 = around 12.5</result>