SUDOKU

Write a number from 1 to 9 into each empty square in the grid so that every number from 1 to 9 appears exactly once in each horizontal row, each vertical column, and each 3×3 block.
2    1    6    
  5    3    9  
    3    6    4
8    4    9    
  4    7    8  
    2    9    1
5    9    2    
  8    6    7  
    4    7    6
* Easy