Let the total freight be Y yuan, and the amount of chemical fertilizer transported from City A to Township C is X tons, so the amount of chemical fertilizer transported to Township D is (200-x) tons; The amount of chemical fertilizer transported from City B to Township C and Township D is (240-x) tons and (60+x) tons respectively. Then the equation is listed according to the relationship between total freight and traffic volume, and finally the minimum value of y is found according to the range of X.

Solve the problem:

Solution: Let the total freight be Y yuan, the amount of chemical fertilizer transported from City A to Township C is X tons, and the amount of chemical fertilizer transported to Township D is (200-x) tons; The amount of chemical fertilizer transported from city B to townships C and D is (240-x) tons and (60+x) tons respectively.

As can be seen from the relationship between the total freight volume and the traffic volume, the functional relationship between Y and X is

y = 20x+25(200-x)+ 15(240-x)+254(60+x)

Simplified y=4x+ 10040(0≤x≤200)

It can be seen from the analytical formula and the image that when x=0, the minimum value of y is 10040.

Therefore, 0 tons will be transported from City A to Township C, and 200 tons will be transported to Township D; Transport 240 tons from B city to C township and 60 tons to D township. At this time, the total freight is the least, and the lowest total freight is 10040 yuan.