On Sunday, Naughty, Xiaoxiao and Smart Dog went climbing together. It took them 3.3 hours to go up the mountain from point A, cross the top of the mountain and descend to point B, and they walked a total of 10.5 kilometers. They go up the mountain at 3 kilometers per hour and down the mountain at 3.5 kilometers per hour. They played at B for a while, and they were going to return along the original road. How long would it take to go from B to A through the original road at the same speed as they went up and down the mountain?
星期天，淘气、笑笑和机灵狗一起去爬山．她们从A地上山，越过山顶下山到B地用了3.3小时，共走了10.5千米．她们上山每小时3千米，下山每小时3.5千米．她们在B地玩了一会儿，准备沿原路返回，按上、下山的原速从B地经过原路上山越过山顶返回A地，需用多少时间？
<gadget id="calculator">3.3 * 3</gadget>
<output>9.9</output>

<gadget id="calculator">10.5 - 9.9</gadget>
<output>0.6</output>

<gadget id="calculator">3.5 - 3</gadget>
<output>0.5</output>

<gadget id="calculator">0.6 / 0.5</gadget>
<output>1.2</output>

<gadget id="calculator">3.3 - 1.2</gadget>
<output>2.1</output>

<gadget id="calculator">3 * 2.1</gadget>
<output>6.3</output>

<gadget id="calculator">10.5 - 6.3</gadget>
<output>4.2</output>

<gadget id="calculator">4.2 / 3</gadget>
<output>1.4</output>

<gadget id="calculator">2.1 / 3.5</gadget>
<output>0.6</output>

<gadget id="calculator">3 * 0.6</gadget>
<output>1.8</output>

<gadget id="calculator">1.4 + 1.8</gadget>
<output>3.2</output>

<result>3.2</result>