First. Two ships, B, set off from port A at the same time, sail upstream to port B, and return immediately after arriving. Their downstream speeds are 1 (1/3) times of their upstream speeds. One hour later, the two ships meet at a distance of 4 kilometers from port B; when ship B arrives at port B, ship A has returned to the midpoint between port A and port B. How many hours does it take for ship A to travel back to port A?
甲．乙两船同时从A港出发，逆流而上向B港驶去，到达后都立即返回．它们的顺水速度都是逆水速度的1(1/3)倍．1小时后两船在离B港4千米处相遇；当乙船到达B港时，甲船已返回至A、B两港的中点．甲船要返回A港还需行驶多少小时？
<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

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

<gadget id="calculator">4 + 3</gadget>
<output>7</output>

<gadget id="calculator">11 - 8</gadget>
<output>3</output>

<gadget id="calculator">7 / 3</gadget>
<output>7/3 = around 2.333333</output>

<gadget id="calculator">(7/3) * 8</gadget>
<output>56/3 = around 18.666667</output>

<gadget id="calculator">(56/3) + 4</gadget>
<output>68/3 = around 22.666667</output>

<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(68/3) + 3</gadget>
<output>77/3 = around 25.666667</output>

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

<gadget id="calculator">(77/3) * (4/3)</gadget>
<output>308/9 = around 34.222222</output>

<gadget id="calculator">1 / (308/9)</gadget>
<output>9/308 = around 0.029221</output>

<gadget id="calculator">(68/3) * (1/2) * (9/308)</gadget>
<output>51/154 = around 0.331169</output>

<result>51/154 = around 0.331169</result>