This is a Consecutive Sudoku starting grid, and we can fill in the hilighted cells. The easiest cells to
                start with in a Consecutive Sudoku are those that are 'consecutive' with a 1 or a 9 - there is only
                one possible solution in this situation, either a 2 or a 8 respectively. We can use this to fill in
                the top and bottom highlighted cells.
            
            
                The highlighted cell to fill in on the center-right is a little trickier to fill in. We can use the
                normal rules of Sudoku to eliminate 1, 2, 3, 4, 6, 7, and 8. This leaves us with just 5 and 9. We
                also know that this number be must be consecutive with 6, i.e. 5 or 7. This allows us to fill this
                cell in with a 5.