Feedback Amplifier Analysis (solution is provided, looking for more conceptul help)

The solution to this problem is provided. I'm mainly just looking for clarification on some things. I don't understand why the 10k (Rs - it's not actually labeled Rs but it's the one in series with Vs) resistance is not being taken into account in parts (e) & (f) and then in part (i) a completely different Ri is being used to calculate Rif and then when they do Rin` they just add on the 10k Rs and put the other 10k in parallel with the previous Rin. How is this possible? I've always taken Rs into account before in all cases.

Also (in general) when calculating the gain for just the basic amplifier, are there situation where resistors after the op-amp (ie. in parallel with Rl) would ever be taken into account?