Two people, A and B, are walking towards each other from two places at the same time. A travels 4.2 kilometers per hour, and B travels 3.8 kilometers per hour. The two met at a distance of 0.5 kilometers from the midpoint of the journey. How many kilometers is the whole journey?
甲、乙两人同时分别从两地相向而行，甲每小时走4.2千米，乙每小时3.8千米．两人相遇时距全程中点0.5千米处．求全程多少千米？
<gadget id="calculator">4.2 - 3.8</gadget>
<output>0.4</output>

<gadget id="calculator">2 / 0.4</gadget>
<output>5</output>

<gadget id="calculator">4.2 + 3.8</gadget>
<output>8</output>

<gadget id="calculator">0.5 * 5 * 8</gadget>
<output>20</output>

<result>20</result>