This summer, Typhoon Fete brought great disaster to Ningbo, especially Yuyao. In order to support the disaster area, the Ningbo municipal government organized

(1) Suppose there are x vehicles transporting food, y vehicles transporting medicines and (20-x-y) vehicles transporting daily necessities.

6x+5y+4(20-x-y)= 100，

y =-2x+20；

(2) Starting from (1), there are X vehicles transporting food, (20-2x) vehicles transporting medicines and X vehicles transporting daily necessities.

x≥5？ ①20? 2x？ ≥4? ②,

The solution is 5≤x≤8,

X is an integer,

The value of x is 5, 6, 7, 8,

There are four arrangements: ① five vehicles for transporting food, five vehicles for transporting drugs 10, and five vehicles for transporting daily necessities;

② 6 vehicles for transporting food, 8 vehicles for transporting medicines and 6 vehicles for transporting daily necessities;

③ 7 vehicles for transporting food, 6 vehicles for transporting drugs and 7 vehicles for transporting daily necessities;

(4) 8 vehicles for transporting food, 4 vehicles for transporting medicines and 8 vehicles for transporting daily necessities;

(3) Let the total freight be W yuan.

w = 6x× 120+5×(20-2x)× 100+4x× 100 = 16000-480 x

∫k =-480 < 0，

W decreases with the increase of x,

Therefore, scheme ④ is selected.

W at least =16000-480× 8 =12160 (yuan).