100 HARD Sudoku Puzzle Book for Kids: 120 Pages, Ages 8 -12 | 100 Sudoku Puzzles for Kids, 9x9, With Solutions, Hard Sudoku Puzzle Book, Improve Your Game with Increasing Difficulty and Solutions
600 Sudoku Puzzles - Expert Level: Ultimate Sudoku Puzzle Book Challenge with Plenty of Very Hard Sudoku Grids with Solutions for Adults, Seniors and Teens