A barrel of oil uses up 75% of the total, and another 85 kg is bought. At this time, the quality of the oil is just the original (6/7). How many kg of oil are there?
一桶油用去总数的75%，又买来85千克，这时油的质量恰好是原来的(6/7)，原来有油多少千克？
<gadget id="calculator">6 / 7</gadget>
<output>6/7 = around 0.857143</output>

<gadget id="calculator">75 / 100</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">1 - (3/4)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(6/7) - (1/4)</gadget>
<output>17/28 = around 0.607143</output>

<gadget id="calculator">85 / (17/28)</gadget>
<output>140</output>

<result>140</result>