I'm trying to self-study this problem. This chapter explained the delta-to-y transformation but I can't seem to find one here.
My best guess is that both resistors on the right are short-circuited which gives them a value of 0. Then you add the two 3 ohm resistor on the left together, and thus the answer 6 ohms.
But I don't know if this is true.
Best Answer
You're right. The three resistors 3 \$\Omega\$, are shorted, so that the equivalent resistance is the sum 3 + 3 = 6.