Solution: Assume that X tons of chemical fertilizer is transported from A to C, 200-X tons of chemical fertilizer is transported from A to D, 240-X tons of chemical fertilizer is transported from B to C, and 260-(200-X) tons of chemical fertilizer is transported from B to D (it is best to make a list), and the total freight is adjusted to Y tons.

y = 20X+25(200-X)+ 15(240-X)+24(X+60)

=4X+ 10040(0≤X≤200)

∫K = 4 > 0

When X=0, y is the smallest.

0 tons from a to c, 200 tons from a to d.

B to C is 240 tons, and B is 60 tons.