I'm having a hard time with this problem

A grass field is shaped like a rectangle with semicircles on both ends. The total length of the field is exactly 100 feet. How wide, to the nearest tenth of a foot, should the field be if its total area is 4,000 square feet?

Can I assume the radius of the circle is 1/2 of the width of the rectangle?

And I still am not seeing how I could solve this