Each letter below stands for a different digit 0 through 9. Determine the code for each square so that the resulting numbers in each row and column are in arithmetic progression, with the middle number being the average of the other two. The code will be different for each puzzle. The first puzzle is solved as an example.

1. | 2. | 3. |

4. | 5. | 6. |

7. | 8. | 9. |

The solutions are here.