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Addition Equation Sudoku

Stage: 3, 4 and 5 Challenge Level: Challenge Level:1
If I label the cells like a coordinate grid, with the bottom left cell as (1, 1) and the top right as (9, 9) then one way of starting is listed below. Can you explain the logic at each step?

(6, 2) (1, 2) (4, 2) (1, 4) (2, 4) (2, 3) (6, 6) (5, 6) (5, 8) (9, 8) (4, 8) (4, 7) (7, 7) (7, 3) (8, 3) (9, 5) (8, 5) (8, 1) (3, 1) (3, 9) (3, 7) (7, 1) (5, 7) (4, 1) (7, 8) (9, 4) (2, 2) (1, 5) (8, 4) (8, 6)