Xiaohua, Xiaohong, and Xiaoli are playing a passing game. If Xiaohua starts to pass the ball and the ball returns to Xiaohua after 4 times, how many different ways of passing the ball are there?
小华、小红、小丽三人进行传球游戏，如果小华开始传球，经过4次后球又回到小华手中，则不同的传球方式共有多少种．
<gadget id="calculator">3 + 3</gadget>
<output>6</output>

<result>6</result>