The frame is a rectangle with a rectangle cut out of it. The area of the frame is 4*6=24 square inches. So the area of the big rectangle (frame and picture) is 48 square inches. (Draw a picture and it will help.) Let's call the width of the frame x. So the distance from the edge of the picture to the edge of the frame is x at any edge. So the equation is (6+2x)(4+2x)=48. Expand this and solve for x and you get x=-6,1. x is a distance, so it must be 1. So the frame is 1 inch wide.
