and B start climbing from the foot of the mountain at the same time, and descend immediately after reaching the top of the mountain. The downhill speed of both of them is 1.5 times of their uphill speed. And A is faster than B. Two hours after the start, A and B meet at a distance of 400 meters from the top of the mountain. When B reaches the top of the mountain, A happens to be halfway down the mountain. So how many hours does it take for A to return to the starting point?
甲、乙两人同时从山脚开始爬山，到达山顶后立即下山．他们两人的下山速度都是各自上山速度的1.5倍．且甲比乙快，开始2小时后，甲与乙在离山顶400米处相遇，当乙到达山顶时，甲恰好下到半山腰．那么甲回到出发点，共用多少小时？
<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">1 - (3/4)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">600 / (1/4)</gadget>
<output>2_400</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 + (1/3)</gadget>
<output>4/3 = around 1.333333</output>

<gadget id="calculator">(4/3) / 1</gadget>
<output>4/3 = around 1.333333</output>

<gadget id="calculator">(4/3) * 1.5</gadget>
<output>2</output>

<gadget id="calculator">1 + 2</gadget>
<output>3</output>

<gadget id="calculator">(1/4) * (1/3)</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">(3/4) + (1/12)</gadget>
<output>5/6 = around 0.833333</output>

<gadget id="calculator">2_400 * (4/3) * 1.5 * (3/4) * (5/6) * (4/3) * 1.5</gadget>
<output>6_000</output>

<gadget id="calculator">(3/4) / 6_000</gadget>
<output>1/8_000 = around 0.000125</output>

<gadget id="calculator">1 * 2_400 * (4/3) * 1.5 * (1/8_000)</gadget>
<output>0.6</output>

<gadget id="calculator">1 + 0.6</gadget>
<output>1.6</output>

<result>1.6</result>