There are two identical red balls and green balls in the pocket, how many possibilities are there to draw 2 balls from the pocket?
口袋里分别有两个相同的红球，绿球，从里摸出2个球，有多少种可能．
<gadget id="calculator">2 * 2</gadget>
<output>4</output>

<gadget id="calculator">1 + 1 + 4</gadget>
<output>6</output>

<result>6</result>