The graph below shows two linear functions.

Which explanation could be used to verify whether the functions are inverses?

To verify whether two functions are inverses or not, you must:
Lets use f(x)=... and g(x)=...
You must first solve and get your answer of f of g of x or f[g(x)]... lets say our answer is x.
Then you solve g of f of x or g[f(x)]... lets say our answer is x.
Since both of our answers are x in these two, they are inverses. If you have different solutions, the two functions are not inverses.