Uncle Wang has brought in some apples, bananas and oranges. The average number of boxes is 13 boxes, including 14 boxes of apples and 10 boxes of bananas. How many boxes of oranges are brought in?
王大叔运进了一些苹果，香蕉和橘子，平均箱数是13箱，其中苹果14箱，香蕉10箱，运进橘子多少箱．
<gadget id="calculator">13 * 3</gadget>
<output>39</output>

<gadget id="calculator">14 + 10</gadget>
<output>24</output>

<gadget id="calculator">39 - 24</gadget>
<output>15</output>

<result>15</result>