I believe C. Sorry if I’m wrong!
Answer: fg
and
Domain: All real number. All real number or 
Explanation:
fg means product of two given function f(x) and g(x)
where,
and 
Now, we have to find fg
So, fg=
Substitute f(x) and f(x)

Using distributive property simplify above expression and we get,

We can see it is cubic polynomial. So, domain of cubic polynomial is all real number.
Domain: All real number or 
Im not sure what the answer is
Volume of the prism:
width × height × lenght = c³