The answer is 38, because if you take away the 15 he bought afterwards (34-15) you get 19, and then since he sold half his collection you would double that (19×2) and that's 38.
The given function is

The inverse function is

To get the inverse, we swap each x and y coordinate.
The rule is 
So that's why the point (0,1) becomes (1,0) for instance.
no
the table does not represent a proportional relationship.
5(z-4)-z=4z-20
5z-20-z=4z-20
4z=4z
z=z
The answer is C