There are 40 liters of water in the two buckets. If you pour 7 liters of water from the first bucket into the second bucket, the water in the two buckets will be the same. How many liters of water is there in the first bucket?
两个桶里共盛水40升，如果把第一桶里的水倒7升到第二个桶里，则两个桶里的水就一样多了，则第一桶有水多少升．
<gadget id="calculator">40 / 2</gadget>
<output>20</output>

<gadget id="calculator">20 + 7</gadget>
<output>27</output>

<result>27</result>