On a map with a scale of 1:3000000, the distance between A and B ports is 12cm. A freighter departs at 7:00 a.m. and sails from A port to B port at a speed of 24km per hour. The time it arrives at B port is how long
在比例尺是1：3000000的地图上，量得A、B两港距离为12cm，一艘货轮于上午7时出发，以每小时24km的速度从A港开向B港，到达B港的时间是多少时
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