The DNA base pairs:
A goes with T.
C goes with G.
If one side has A, the other will have T, and vice versa.
If one side has C, the other will have G, and vice versa.
C C G T A G G C C
| | | | | | | | |
G G C A T C C G G
So the sequence of the right chain would be GGCATCCGG.