Please add a condition to the following question before answering. There is a barrel of oil, 14 kilograms are used on the first day, how much. (3/7) of the total amount was used the next day, how many kilograms were used the next day?
请在下面题目中补充一个条件后，再解答．有一桶油，第一天用去14千克，多少．第二天用了总数的(3/7)，第二天用了多少千克？
<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<result>2/7 = around 0.285714</result>