You just need to substitute the the given function. So if f(-8) then you fill in f(n)=2n+4 which would be f(-8)=2(-8)+4. Which is -12.
hope this helps !
I’m not sure I only answer these for the points :)
Yes What do you need help with ?
This is a composite. Another way to write them is f(g(x)). Take the function g(x) and stick it in for x in f(x). Like this:

. But we aren't done cuz there's some simplifying there to do.

and canceling out the 3's we get just a simple x as our answer. The choice is the last one above as your answer.