So how? vs How so?

Please put them into what you think are acceptable contexts. As they stand, the first asks how and the 2nd asks why.

Okay.

Person A: Are you playing dumb or plain stupid?

Person C: Stupid, my foot! You're the stupid one.

Person A: It's money, of course.

Person C: Money can makes the world go round. How come you don't understand such a simple concept?

Person B: Exactly.

Person C: Money?

Person C: You want money for this?

Person A: Of course.

Well, unfortunately I do not understand the drift of the conversation, so I will just comment using the last few turns:

Person C: Money? You want money for this?

Person A: Of course.

Person B: So how? <--- Is this correct?-- No, I don't know what B means by this remark. What is B's intent?

To ask C if he wants to give the money or not.

In that case, both So how and How so are wrong there; neither of them mean that. Let me give you 2 examples:

A: I never graduated from high school, but now I'm manager at the bank.

B: How so?

A: Because my uncle's the president.

C: I didn't read the book to find out what happened.

D: So how? -- Note that this is very informal; D w

I see.

What would the correct phrase to use there?

Thanks.

Perhaps this:

Person C: Money? You want money for this?

Person A: Of course.

Person B: So are you going to / do you want to?

Thanks so much.