answer:At the time of the first meeting, if the ferries left from opposite shores, the combined distance travelled will be exactly one width of the river. At the time of the second meeting, each boat will have travelled one complete width of the river, plus together they will have travelled a third width. The time taken before the ferries meet again must be three times the time taken to meet the first time as they will have travelled exactly three times the distance at the same speed. This means the ferry that had travelled 700 feet at the time of the first meeting has had time to travel 2,100 feet by the time of the second meeting. This ferry is now 400 feet from the shore on its way back to where it started so the river’s width must be 2,100 – 400 = 1,700 feet.