Delta-Star Combination Exercise
I figured it out, this is the answer for part(b) &quot;Finding Equivalent resistance from A to N&quot;.
First of all, here is a nicer sketch:

Now we will focus at the delta connection defined by N , B , C :

And now if we go back to our original sketch and replace the converted circuit we can greatly simplify it:

Finally, we are ready to compute the equivalent resistance from A to N: