The elder brother and the younger sister have a total of 20 pieces of drawing paper. After the elder brother gives the younger sister 4 sheets, the number of them is equal. How many sheets did the younger sister have?
哥哥和妹妹共有20张图画纸，哥哥给妹妹4张后，两人的张数相等，妹妹原来有多少张．
<gadget id="calculator">4 * 2</gadget>
<output>8</output>

<gadget id="calculator">20 - 8</gadget>
<output>12</output>

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

<result>6</result>