The Geo-8X, 9X, and 10X Puzzles have an added feature. Some cells contain Red, Blue or Green Underlines.
Find the Numbers in the cells with the Red Underlines first. All these can be determined with the starting numbers in the grid.
Then find all the Numbers in the cells with the Blue Underlines. This can be done because you have added numbers in the Red Underlined cells.
Next, find the Numbers in the cells with the Green Underlines. Remember when you determine what numbers can’t be in a cell sometimes there is only One Number left. Also, look at the entire Row or Column, and figure out what numbers are missing. Some of those missing numbers might fit in only one cell.
Now, you can finish the puzzle. As always, you never have to guess, there is ALWAYS a CLUE somewhere.