Answer
a) $f(6)=8$
b) $x=-6$
c) $\text{Domain: all real numbers}
\\\text{Range: all real numbers}
$
Work Step by Step
a) Based on the graph, when $x=6,$ the value of $y$ or $f(x)$ is $8.$ Hence, $
f(6)=8
.$
b) Based on the graph, when $y$ or $f(x)$ is $0,$ the value of $x$ is $
x=-6
.$
c) Based on the graph, the values of $x$ and $y$ can be any real number. Hence,
\begin{array}{l}\require{cancel}
\text{Domain: all real numbers}
\\\text{Range: all real numbers}
.\end{array}