In circle O, chords AB and CD are congruent. Ab measures 2x + y, while CD measures 16.5
Two other chords are congruent. GH equals x +2y and KL equals 13.5
I set them up like this 2x + y = 16.5
x+2y = 13.5
then I substituted-rewrote it x = 13.5-2y
Then substituted
2(13.5) + y = 16.5
y = 3.5 and then subbed it back in to equation and came up with x = 6.5
Is this correct, I think it is but I want to make sure
Yes, I agree with your procedure and answer. But you didn't copy it correctly when it was posted.
2(13.5) + y = 16.5 should be:
2(13.5 - 2y) + y = 16.5,
27 - 4y + y = 16.5,
-3y = 16.5 - 27 = - 10.5,
y = 3.5.