B-D freight: 18(300-X)

Freight for A-C: 20(240-X)

A-D freight: 25260-(300-X)

w = 15X+ 18(300-X)+20(240-X)+25260-(300-X)

That is W=2X+9200.

You'd better do it again ... it's good for you ~)

... you should understand ...