Cost of fencing a rectangular lot with unequal side costs

[you_of_eh]

Fencing around a rectangular parking lot costs twice as much along the side facing the street than the other three sides. The fencing along the back of the lot costs $10 per meter. Express the cost C of the fence as a function of the width w if the length of the street side of the parking lot is 20m longer than the width.

Here is the best I could come up with..

C(w)=(3w+2/3w)$10+(w+2/3w)$20

How does that look?

 

[you_of_eh]

2nd attempt..

C(w)=$10/m(5w+60m)