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.
4    7    2    
  9    1    6  
    8    3    7
1    9    6    
  6    5    7  
    7          8
8    1    7    
  1    4        
    9    2    4
** Moderate