Dongdong has 30 colored pens, and Jiumei has 15 colored pens. After Jiumei gave Dongdong as many colored pens, Dongdong's number of colored pens was exactly 4 times that of Jiumei.
东东有彩笔30支，九妹有彩笔15支．九妹把多少支彩笔给东东后，东东的彩笔支数正好是九妹的4倍．
<gadget id="calculator">30 + 15</gadget>
<output>45</output>

<gadget id="calculator">4 + 1</gadget>
<output>5</output>

<gadget id="calculator">45 / 5</gadget>
<output>9</output>

<gadget id="calculator">15 - 9</gadget>
<output>6</output>

<result>6</result>