Answer
See the explanation below.
Work Step by Step
(a)
According the given function
$f\left( x \right)=5-7x$.
So, to find $f\left( 4 \right)$ put $x=4$ in function $f\left( x \right)=5-7x$.
$\begin{align}
& f\left( x \right)=5-7x \\
& f\left( 4 \right)=5-7\left( 4 \right) \\
& =5-28 \\
& =-23
\end{align}$
(b)
Given function $f\left( x \right)=5-7x$.
To find $f\left( x+3 \right)$ put $x=x+3$ in function $f\left( x \right)=5-7x$.
$\begin{align}
& f\left( x \right)=5-7x \\
& f\left( x+3 \right)=5-7\left( x+3 \right) \\
& =5-7x-21 \\
& =-7x-16
\end{align}$
(c)
Given function
$f\left( x \right)=5-7x$.
To find $f\left( -x \right)$ put $x=-x$ in function $f\left( x \right)=5-7x$.
$\begin{align}
& f\left( x \right)=5-7x \\
& f\left( -x \right)=5-7\left( -x \right) \\
& =5+7x \\
& =7x+5
\end{align}$
Thus, the value of $f\left( -x \right)=7x+5$.
