a) Line 1 assigns $x$ and line 2 assigns $y$ using $x$, therefore $y=\\var{{a}+{x}}$.
Line 3 is a calculation that uses $y$ but never reassigns any of the variables.
Line 4 then overwrites $x$ using $y$. Therefore $x=\\var{{a}+{b}+{x}}$.
b) The value of $z$ is the same as the value of $x$.
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