There is a grain warehouse that stores 78 tons of grain, and 31 tons are shipped out on the first day. After some of the grain is shipped out the next morning, it is shipped in again in the afternoon. The grain shipped in the afternoon is exactly equal to the weight of the rest in the morning. There are 64 tons of grain, how many tons were shipped out the next morning.
有一个粮食仓库存粮78吨，第一天运出31吨，第二天上午运出一部分后，下午又运进粮食，下午运进的粮食正好与上午剩下的重量相等，这时仓库里共存有粮食64吨，第二天上午运出了多少吨．
<gadget id="calculator">78 - 31</gadget>
<output>47</output>

<gadget id="calculator">64 / 2</gadget>
<output>32</output>

<gadget id="calculator">47 - 32</gadget>
<output>15</output>

<result>15</result>