solve

 sudoku

I pick up the easy numbers first by working through 1 to 9 in the rows of boxes then the columns of boxes.

c2r1 must be 8 because of the 8's in boxes 2, 3 and 7. The rules allow for only one 8 in any box and any row or column but box 1 must have an 8. I'll stop colouring the row/columns now as you've got the idea.

c1r4 must be 4 due to the 4's in boxes 5, 6 and 7

The 4's in boxes 6, 7 and 8 make 4 in box 9.