Answer
$$f(2,-1)=12,\ f(-4,1)=-6,\ f(-2,-3)=10,\ f(0,8)=-19$$
Work Step by Step
Since $$f(x, y)=2 x-3 y+5$$
Then
\begin{align*}
f(2,-1)&==2 (2)-3 (-1)+5\\
&=12
\end{align*}
and
\begin{align*}
f(-4,1)&==2 (-4)-3 (1)+5\\
&=-6
\end{align*}
\begin{align*}
f(-2,-3)&==2 (-2)-3 (-3)+5\\
&=10
\end{align*}
\begin{align*}
f(0,8)&==2 (0)-3 (8)+5\\
&=-19
\end{align*}
