4. A new parking lot is twice the area of the old one. If the length of the old one is 100 ft more than the width and the width is the same as it was, what are the dimensions of the lot?

And now the really hard ones...

1. The area of a rectangular field is 1200 m^2. Two parallel sides are fenced with aluminum at $20/m. The remaining two sides are fenced with steel at $10/m. If the cost of the fencing is $2200, what is the length of each side fenced with aluminum? What is the length of each side fenced with steel?