B 30-X units are shipped to A, and B 26-(32-X)=X-6 units are shipped to B.

y = 400 X+300(32-X)+200(30-X)+500(X-6)

= 400 x+9600-300 x+6000-200 x+500 x-3000

=400X+ 12600

(2) because the coefficient before x is greater than 0, y increases with the increase of x.

So when x is the smallest, the cost is the lowest.

So try to transport the bulldozers in A to B. B only needs 26 bulldozers, all of which are transported by A..

Then at this time a is transported to A: X=32-26=6.

The cost is 400× 6+12600 =15000 yuan.