There are 6 red balloons and 4 yellow balloons. The number of yellow balloons remains the same. How many red balloons are added, the number of red balloons is 3 times that of yellow balloons.
红气球有6个，黄气球有4个，黄气球个数不变，再添多少个红气球，红气球的个数就是黄气球的3倍．
<gadget id="calculator">4 * 3</gadget>
<output>12</output>

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

<result>6</result>