The mass of a barrel of oil is 56kg, and the mass of the barrel and oil after pouring out half is 29.4kg. What is the mass of this barrel of oil?
一桶油连桶的质量为56kg，倒掉一半后连桶带油的质量为29.4kg，这桶油的质量是多少千克？
<gadget id="calculator">56 - 29.4</gadget>
<output>26.6</output>

<gadget id="calculator">26.6 * 2</gadget>
<output>53.2</output>

<result>53.2</result>