You want to place a towel bar that is 24 1⁄4 centimeters long in the center of a door that is 70 1⁄3 centimeters wide. how far should you place the bar from each edge of the door?

Think of it like this to make it easy to understand: If you lined the edge of the towel bar up with the edge of the door, the towel bar will take up 24.25 cm of the width of the door, leaving 46.083 cm free of towel bar.  So if you want the bar to be in the middle of the door, divide the 46.083 in half to get that 23.042 cm would be what's on each side of the bar if it is in the middle of the door.