( 1)400 X+800( 10-X)+300(6-X)+500(X-2)= 8000
400 x+8000-800 x+ 1800-300 x+500 x- 1000 = 8000
-200X=-800, X=4, Beijing to Wuhan 4, Chongqing 6; Shanghai to Wuhan 2, Taiwan Province, Chongqing 2) Taiwan Province,
(2)6-X & lt； =4，X & gt=2，X-2 & lt； =4，X & lt=6，2≤X≤6；
That is, from Beijing to Wuhan, X=2, 3, 4, 5, 6, 8, 7, 6, 5, 4, 5, 6 to Chongqing,
Shanghai to Wuhan (6-x) = 4, 3, 2, 1, 0, Chongqing 0, 1, 2, 3, 4,
(3) If the total freight is Y and Beijing sends it to Wuhan X, then,
y = 400 X+8000-800 X+ 1800-300 X+500 X- 1000 =-200 X+8800(，2≤X≤6)
When X=6, y is the lowest, that is, X=6, and the lowest freight Y=-200*6+8800=7600 yuan.
That is, Beijing to Wuhan 6, Chongqing 4, Shanghai to Wuhan 0, Chongqing 4, the lowest freight.