Okay I have two arrays

face *A[21];

face *B[21];

i need to put positions 0-3-6-9-12-15-18 of A into 0 through 6 of B

1-4-7-10-13-14-19 of A into 7 through 13 of B and 2-5-8-11-14-21 of A into 14-20 of B.

I can't figure out how to do this, any help you can offer will be greatly appreciated.