It takes 5 hours for an express train to travel from point A to point B, and 7 hours for a slow train to travel from point B to point A. Now the two cars leave oppositely from stations A and B at the same time. It is known that the express train travels 24 kilometers more per hour than the slow train. Find the total journey time How many kilometers is it?
一辆快车从甲地到乙地需5小时，一列慢车从乙地到甲地需要7小时，现在两车同时从甲乙两站相对开出，已知快车比慢车每小时多行24km，求全程是多少千米？
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 / 7</gadget>
<output>1/7 = around 0.142857</output>

<gadget id="calculator">(1/5) - (1/7)</gadget>
<output>2/35 = around 0.057143</output>

<gadget id="calculator">24 / (2/35)</gadget>
<output>420</output>

<result>420</result>