person walked from the foot of the mountain to the top of the mountain, and then climbed over the top of the mountain and walked down the mountain for a total of 31.5 kilometers. It took 6.6 hours, and his speed up the mountain was 4.5 kilometers per hour, and his speed down the mountain was 5 kilometers per hour. If he Then go back along the original road to the top of the mountain, and climb over the top of the mountain and walk down the mountain, and the speed of going up and down the mountain remains the same, so how many hours will it take him to return?
某人从山脚走到山顶，再翻过山顶走下山共行了31.5千米，用了6.6小时，并且他上山的速度是每小时4.5千米，下山的速度是每小时5千米，如果他再沿原路返回走到山顶，并翻过山顶走下山，且上山、下山的速度不变，那么他返回一共需多少小时？
<gadget id="calculator">33 - 31.5</gadget>
<output>1.5</output>

<gadget id="calculator">1.5 / 0.5</gadget>
<output>3</output>

<gadget id="calculator">6.6 - 3</gadget>
<output>3.6</output>

<gadget id="calculator">5 * 3.6</gadget>
<output>18</output>

<gadget id="calculator">18 / 4.5</gadget>
<output>4</output>

<gadget id="calculator">4.5 * 3</gadget>
<output>13.5</output>

<gadget id="calculator">13.5 / 5</gadget>
<output>2.7</output>

<gadget id="calculator">4 + 2.7</gadget>
<output>6.7</output>

<result>6.7</result>