The younger sister has twice as many glass balls as the older brother. After the younger sister gives the older brother three, the older brother and the younger sister have the same number of glass balls. How many glass balls did the younger sister originally have?
妹妹的玻璃球个数是哥哥的2倍，妹妹给哥哥3个后，哥哥和妹妹的个数相等，妹妹原来有多少个玻璃球．
<gadget id="calculator">3 + 3</gadget>
<output>6</output>

<gadget id="calculator">2 - 1</gadget>
<output>1</output>

<gadget id="calculator">6 / 1</gadget>
<output>6</output>

<gadget id="calculator">6 * 2</gadget>
<output>12</output>

<result>12</result>