Add up the numbers! At the end of each line is a number in a white bubble. Click and drag the numbered tiles along the tracks so they add up to the numbers in the white bubbles. The numbers in the white bubbles will always correspond to a particular row or column. You can see what the numbers in that row or column are currently adding up to in the unfilled circle at the other end of the line.

If two numbers are next to each other on the track, you can swap their positions by moving one into the other.

If you get stuck and need help, click on the question mark to get a hint. You only have a limited amount of hints, though!