Chubby makes nonstandard checkerboards that have 31 squares on each side. The checkerboards have a black square in every corner and alternate red and black squares along every row and column. How many black squares are there on such a checkerboard?<spanclass=′latex−bold′>(A)</span>480<spanclass=′latex−bold′>(B)</span>481<spanclass=′latex−bold′>(C)</span>482<spanclass=′latex−bold′>(D)</span>483<spanclass=′latex−bold′>(E)</span>484