In the property palette you can check the area of linear entities. If you want to show that area in your drawing you use the 'Write Area' command. Just select closed linear entities in your drawing. You can set the text height and the precision. The precision defines the amount of decimals the command will use. By default the command will align the text that is placed to the coordinate system. When you run the command it will place a text entity inside every linear entity containing the area of that linear entity.