From city A to city B, the express train takes 12 hours, and the slow train takes 15 hours. If two cars drive from city A to city B at the same time, the express train returns immediately after arriving in city B. After how many hours does it meet the slow train?
从甲城到乙城，快车需要12小时，慢车需要15小时，如果两车同时从甲城开往乙城，快车到达乙城后，立即返回，经过几小时与慢车相遇？
<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">(1/15) * 12</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">1 - (4/5)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">(1/12) + (1/15)</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">(1/5) / (3/20)</gadget>
<output>4/3 = around 1.333333</output>

<result>4/3 = around 1.333333</result>