The two buckets hold 40 catties of water in total. If you pour 7 catties of water from the first bucket into the second bucket, the water in the two buckets will be the same. What is the original volume of water in the first bucket?
两个桶里共盛水40斤，若把第一桶里的水倒7斤到第2个桶里，两个桶里的水就一样多，则第一桶原有多少斤水．
<gadget id="calculator">40 / 2</gadget>
<output>20</output>

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

<result>27</result>