Suppose that $z$ is a linear function of $x$ and $y$ with slope -3 in the $x$ direction and slope 1 in the $y$ direction.

(a) A change of $-0.3$ in $x$ and $0.3$ in $y$ produces what change in $z$?
change in $z =$

(b) If $z=3$ when $x=8$ and $y=5$, what is the value of $z$ when $x=8.1$ and $y=4.9$?
$z =$