Start by calculating the area of the desk. Area of a rectangle is base x height, 5.5 * 3.5 = 19.25 ft^2. Now calculate the area of the tile: .5 * .5 = .25 ft^2. To figure out how many tiles can fit, divide the area of the desk by the area of one tile: 19.25 / .25 = 77 tiles.
