A barrel of oil weighs 45 kilograms, pour out (3/7) of the oil in the barrel, and the weight of the barrel is 27 kilograms. How many kilograms does the barrel weigh?
一桶油连桶重45千克，倒出桶中油的(3/7)，连桶重27千克，桶重多少千克．
<gadget id="calculator">45 - 27</gadget>
<output>18</output>

<gadget id="calculator">3 / 7</gadget>
<output>3/7 = around 0.428571</output>

<gadget id="calculator">18 / (3/7)</gadget>
<output>42</output>

<gadget id="calculator">45 - 42</gadget>
<output>3</output>

<result>3</result>