Answer: 12
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Explanation:
You can use the AAS (angle angle side) theorem to prove that triangle ABD is congruent to triangle CBD.
From there, we can then say that AD and DC are the same length
AD = DC
3y+6 = 5y-18
3y-5y = -18-6
-2y = -24
y = (-24)/(-2)
y = 12
