Answer:
error is in step (1) x and y should be flipped.
Explanation:
Steps to find inverse should be
y = x² + 12x
x = y² + 12y
x + 36 = y² + 12y +36
x + 36 = (y + 6)²

y =

So inverse will be y =

Therefore, error is in step (1) x and y should be flipped.