There are several small balls in boxes A, B, and C. Take 4 balls from box A and put them in box B, and then take 8 balls from box B and put them in box C. The number of small balls in the three boxes is equal. It turns out that box B has more balls than box C?
甲、乙、丙三个盒子各有若干个小球，从甲盒拿出4个放入乙盒，再从乙盒拿出8个放入丙盒后，三个盒子内的小球个数相等．原来乙盒比丙盒多几个球？
<gadget id="calculator">8 - 4</gadget>
<output>4</output>

<gadget id="calculator">4 + 8</gadget>
<output>12</output>

<result>12</result>