If Shanghai transfers to station X in A city, Shanghai transfers to station B 12-x, Hangzhou transfers to station A 10-x, and Hangzhou transfers to station B 6-( 10-x)=x-4.

w = 400 x+800( 12-x)+300( 10-x)+500(x-4)=-200 x+ 10600

Domain of definition

; 4≤x≤ 10

W is

Descending function

When x= 10, w has a minimum value =8600.

That is, 10 was transferred from Shanghai to a city, and 2 were transferred from Shanghai to b city. Hangzhou turns to a city 0 and Hangzhou turns to b city 6.