How or can someone set this up as an equation or what steps do i do?

A garden area is 30ft long and 20ft wide. A path of uniform width is set around the edge. If the remaining garden area is 400ft^2, what is the width of the path?

You submitted this a few days ago along with a frame and picture problem exactly the same type. I told you to look at the frame question that I worked out you.
Are you needing help or a kick in the rear? Success in life depends on a very large extent on not abusing others, standing on your own feet.