You start with today’s start number. Each row contains 9 possible equations.
Choose one equation from row 1, then one from row 2, and continue down the grid.
Your chosen square changes into the new number. Tap it again to undo that row. Changing an earlier row clears later rows.
If you reach the exact target, you score a perfect solve. If you finish all 9 rows but miss the target, you still complete the puzzle and your result shows how far away you were.
There is always at least one hidden path that reaches the target number.