Answer
$z=2$ is extraneous.
Work Step by Step
$-z=\sqrt -z+6$
With $z=-3$ then $-(-3)=\sqrt -(-3)+6$
$3=\sqrt 9$
$3=3$
With $z=2$ then $-(2)=\sqrt -(2)+6$
$-2=\sqrt 4$
$-2\ne 2$
$z=2$ is extraneous.
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