Answer
$$z=9,\:y=33,\:x=15$$
Work Step by Step
Solving the system of equations using substitution, we find:
$$ -\frac{3-\left(2z+15\right)}{2}+2z+15+z=57 \\ z=9 \\ y=2\cdot \:9+15=33 \\ x=-\frac{3-33}{2}=15$$
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