There are less than 50 cards in the box, and there are 3 children on average or 13 children are left with one card. How many cards are there in the box?
盒子里卡片不足50张，平均分给3个小朋友或13个小朋友都剩下一张，盒子里一共有多少张？
<gadget id="calculator">3 * 13</gadget>
<output>39</output>

<gadget id="calculator">39 + 1</gadget>
<output>40</output>

<result>40</result>