Two people, A and B, set off from A to B at the same time at a speed of 4 kilometers per hour. After walking for 2.5 kilometers, A returns to A to pick up the documents, and he rushes to A at a speed of 6 kilometers per hour. After getting the file, they still chased after B at a speed of 6 kilometers per hour, and they arrived at B at the same time. It is known that A has been delayed for 15 minutes in getting the documents in the office, find the distance between A and B.
甲、乙两人同时以每小时4千米的速度从A地出发到B地办事，行走2.5千米后，甲返回A地取文件，他以每小时6千米的速度赶往A地，取到文件后，仍以每小时6千米的速度回头追赶乙，结果他们同时到达B地．已知甲取文件在办公室耽误了15分钟，求A，B两地距离．
<gadget id="calculator">2.5 / 4</gadget>
<output>0.625</output>

<gadget id="calculator">2.5 / 6</gadget>
<output>0.416667</output>

<gadget id="calculator">15 / 60</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">0.625 + 0.416667 + (1/4)</gadget>
<output>1.291667</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">(1/4) - (1/6)</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">1.291667 / (1/12)</gadget>
<output>15.500004</output>

<result>15.500004</result>