Ok to get the maximum amount, start offcourse with the highest number clockwise (9,8,7) in the corners, then counterclockwise, put the next 3 in (6,5,4) and again counterclockwise but start 1 row later (3,2,1). With that you get top row (9,2,4,8) rightrow (8,5,3,7) and left row (9,1,6,7) and all equal 23.