The postman leaves at 9 o'clock in the morning to send a piece of mail to the opposite mountain. From the post office, it takes a 13-kilometer uphill road and an 11-kilometer downhill road. He walked 6 kilometers per hour when going uphill, and 8 kilometers per hour when going downhill. After arriving at the destination and staying for 1.5 hours, he returned from the original road. It took (how many) hours for the postman to go back and forth.
邮递员早晨9时出发送一份邮件到对面山里，从邮局开始要走一段上坡路长13千米，一段下坡路长11千米．他上坡时每小时走6千米，下坡时每小时走8千米，到达目的地停留1.5小时以后，又从原路返回，邮递员来回共用了(多少)小时．
<gadget id="calculator">13 + 11</gadget>
<output>24</output>

<gadget id="calculator">24 / 6</gadget>
<output>4</output>

<gadget id="calculator">24 / 8</gadget>
<output>3</output>

<gadget id="calculator">4 + 3 + 1.5</gadget>
<output>8.5</output>

<result>8.5</result>