Blue Brain Train Sudoku Book, 9x9 Puzzles, 250 Pages, 5x8, Hard

Orange Brain Train Sudoku Book, 9x9 Puzzles, 250 Pages, 5x8, Hard

Yellow Brain Train Sudoku Book, 9x9 Puzzles, 250 Pages, 5x8, Hard

Purple Brain Train Sudoku Book, 9x9 Puzzles, 250 Pages, 5x8, Hard

Green Brain Train Sudoku Book, 9x9 Puzzles, 250 Pages, 5x8, Hard