Complementary DNA strand have the letters switched from each other. That would be:
A -> T OR T -> A
And
C -> G OR G -> C
As well as the direction of the strand:
5’ -> 3’ to 3’ -> 5’
For the first set:
DNA: 5’ - ATTATCGCGTAGCTAGCAGT - 3’
Comp: 3’ - TAATAGCGCATCGATCGTCA - 5’
As you can see the strands are the opposite from one another.
Try out the second set of strands and if you’re still having struggles let me know in the comments (:
