Two survey engineering teams, A and B, set off from two places 28.5km apart and head towards each other. If team A travels 4.5km per hour and team B travels 4km per hour, how long will it take for the two teams to meet?
甲乙两个勘测工程队从相距28.5km的两地出发，相向而行．如果甲队每小时行4.5km，乙队每小时行4km，两队多长时间后相遇？
<gadget id="calculator">4.5 + 4</gadget>
<output>8.5</output>

<gadget id="calculator">28.5 / 8.5</gadget>
<output>3.352941</output>

<result>3.352941</result>