A certain Marine Corps took part in a training activity. It took 4.5 hours to run from A to B, and 6.5 hours to return by the original route. It is known that the distance between A and B is 110 kilometers. Find the average round trip speed of the team.
某海军陆战队参加拉练活动，从甲地跑得到乙地需要4.5小时，原路返回时用了6.5小时，已知甲乙两地的路程为110千米．求该队伍往返的平均速度．
<gadget id="calculator">220 / 11</gadget>
<output>20</output>

<result>20</result>