A factory is to be built on a lot measuring 210 ft by 280 ft. A local building code specifies that a lawn of uniform width and equal in area to the factory must surround the factory.

5 answers

so, draw a diagram, label the dimensions and answer whatever question you have (not shown).
What must the width of the lawn be?
and If the dimensions of the factory are A ft by B ft with A<B, then A=? B=?
something tells me you did not draw a diagram or do much of anything else. The area of the lot is 58800.

So, if the lawn has width w, the factory has dimensions

(210-2w)(280-2w)

and we know that its area is half of the lot. So,

(210-2w)(280-2w) = 58800/2
Now just solve that for w, and you can then find the desired dimensions
Thanks, those are the same results that I got, but I don't know why it keeps giving me a note that it says that my answer is wrong.
I hope you got w=35. Then the dimensions are 140x210

Check:
140*210 = 29400, half of the lot's area.