solve

 sudoku

The 3, then 6 and 5 in the top row all had only one option. ie. if you look at c6r1 and check the known numbers from 1 to 9 already in row1, col6 and box2, the only one missing is 3.

The possible numbers were then updated in associated cells.

The new 3 in row 1 with the 3 in box 1 makes a 3 in box 3 which leaves a 7 in the last cell in the box.

The 7 in box 3 makes a 2 in c6r3.

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