This is an algebra issue - I have written what I thought would be the correct formula for Network C - the computer doesn't like the input method, claims that it failed to parse the equation....
It liked my other two!!
Mind you, this has to be in terms of R
Parallel resistance - there are two parallel circuits.
[(R1*R2)/(R1+R2)]*2
but in terms of R:
[(R^2)(2R)]*2
This is more of a "think like a computer" issue than electrical basics knowledge.