I'm studying for the CQE and I've come across something else in the primer that isn't quite clicking. See the first equation in the attached picture.

I don't really understand the difference between variables B and C and then how they logically fit in the equation-

Cost per sampling* max samples makes sense, but why then would you add to it "cost per inspection unit* average samples"?

So if you had 30 samples from a 500 PC lot and it costed $1 to inspect each one, I see why you would multiple 30*$1, but why would you add something else to it? And in this case what would you add?

My picture is not attaching so the formula given is:

Total Cost= overhead cost + ('cost/unit of sampling' * max sample size) + ('cost/unit of inspecting' * average samples size)