Fill in some of the blank squares with digits 1-9 so that each row and column contains exactly 3 digits, with the middle number in each row and column being the sum of the other two.

A. | B. | C. | D. | E. | F. |

G. | H. | I. | J. | K. |

L. | M. | N. | O. |

P. | Q. | R. |

The solutions are here.