Port A and Port B are 150 kilometers apart. It took a ship 4.5 hours to sail from Port A to Port B. When returning, it took 1 hour longer than when it was going in the opposite direction. What is the average speed of the ship going back and forth?
甲、乙两港相距150千米，一艘轮船从甲港驶往乙港用了4.5小时，返回时因为是逆行，比去时多用了1小时，求这艘轮船往返的平均速度？
<gadget id="calculator">4.5 + 4.5 + 1</gadget>
<output>10</output>

<gadget id="calculator">2 / 10</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">150 * (1/5)</gadget>
<output>30</output>

<result>30</result>