A living room wall is 11 feet long. How far from the corner would you have to the edge of 2ft 6in for shelf for it to be centered on the wall

11 foot wall,

the center of the wall would be 5 1/2 feet which is 5 feet 6 inches

the shelf is 2 feet 6 inches, so the center of that would be 1 foot 3 inches

5 ft 6 in - 1 ft 3 in = 4 ft 3 inches from corner