It takes 4 hours for an express train to travel from city A to city B, and it takes 5 hours for a slow train to arrive from city B to city A. If the slow train travels 2/5 of the whole journey first, the express train will leave. How many hours after the express train leaves? Meet the slow train?
一列快车从甲城开往乙城需要4小时到达，一列慢车从乙城开往甲城需5小时到达，如果慢车先行了全程的(2/5)后，快车才出发，快车出发后几小时与慢车相遇？
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (2/5)</gadget>
<output>3/5 = around 0.6</output>

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

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/4) + (1/5)</gadget>
<output>9/20 = around 0.45</output>

<gadget id="calculator">(3/5) / (9/20)</gadget>
<output>4/3 = around 1.333333</output>

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