Riddle thirteen

Riddle Thirteen: Itchy Knees Son

Difficulty: 5
Interest: 5

This kind of problem has become very common in recent days, especially in newspapers. Finish the problem and solve the equation.

Write the answer as a plain number.

The title is an homophone of 'ichi ni san', which means 'one two three' in Japanese.

Next Level

*Spoilers*

This is effectively a sudoku puzzle. You can either do it manually, or search google for a sudoku solver. Solve the equation by adding each number in the diagonal line from top left to bottom right. Write the two digits and .html to go to the next puzzle.