A and B start from A and B respectively at the same time and walk toward each other. If both of them travel at the original speed, they can meet each other in 3 hours. Now A travels 1 km less per hour than the original plan, and B travels 0.5 km less per hour than the original plan. As a result, the two met in 4 hours. What is the distance between A and B in miles?
甲、乙两人分别从A、B两地同时出发，相向而行．如果两人都按照原定速度行进，3小时可以相遇．现在甲比原计划每小时少走1千米，乙比原计划每小时少走0.5千米，结果两人用了4小时相遇．A、B两地相距多少千米．
<gadget id="calculator">1 + 0.5</gadget>
<output>1.5</output>

<gadget id="calculator">4 - 3</gadget>
<output>1</output>

<gadget id="calculator">1.5 / 1</gadget>
<output>1.5</output>

<gadget id="calculator">3 * 1.5</gadget>
<output>4.5</output>

<gadget id="calculator">4.5 + 1 + 0.5</gadget>
<output>6</output>

<gadget id="calculator">6 * 3</gadget>
<output>18</output>

<result>18</result>