Select the digits from 1 to 9 in the grid once each so that each row and column adds up to 9 or less.
• Tap once to remove a number.
• Tap twice to circle a number.
Only nine squares will remain; not every row and column needs to have a number in it, and some rows and columns will add up to less to 9.
You never have to guess. Logic will always be enough to solve.