Example 1: Two people, A and B, start from two places 20 kilometers apart at the same time and walk toward each other. A walks 6 kilometers per hour, and B walks 4 kilometers per hour. How many hours later did the two meet?
例1：甲乙两人分别从相距20千米的两地同时出发相向而行，甲每小时走6千米，乙每小时走4千米．两人几小时后相遇？
<gadget id="calculator">6 + 4</gadget>
<output>10</output>

<gadget id="calculator">20 / 10</gadget>
<output>2</output>

<result>2</result>