How to Solve SUM DOKU puzzles To solve SUM DOKU puzzle, enter numbers into the diagram so that every row, every column, and every small 9-box square within the larger diagram (there are 9 of these) contains the numbers 1 through 0. Note however, that each puzzle contains areas surrounded by dotted lines, each with a small number in the upper left corner. The digits you enter into each of these areas, called cages, must add up to the number in the corner, and all of the digits in each of these areas must be different from one another. Since cages may cross over heavy lines, they can contain digits from more than one 9-box square.