The mass ratio of A and B barrels of oil is 9:5. If 20 kg of oil in A barrel is poured into B barrel, the mass ratio of A and B barrels of oil is 4:3. So how many kilograms of oil is in barrel A?
甲、乙两桶油的质量比为9：5，如果把甲桶中的20千克油倒入乙桶，这时甲、乙两桶油的质量比为4：3．那么原来甲桶有多少千克油．
<gadget id="calculator">9 + 5</gadget>
<output>14</output>

<gadget id="calculator">9 / 14</gadget>
<output>9/14 = around 0.642857</output>

<gadget id="calculator">4 + 3</gadget>
<output>7</output>

<gadget id="calculator">4 / 7</gadget>
<output>4/7 = around 0.571429</output>

<gadget id="calculator">(9/14) - (4/7)</gadget>
<output>1/14 = around 0.071429</output>

<gadget id="calculator">20 / (1/14) / 14</gadget>
<output>20</output>

<gadget id="calculator">20 * 9</gadget>
<output>180</output>

<result>180</result>