Equivalent resistance via series-parallel reduction Steps:

• Identify the two parallel paths between X and Y: one single 6Ω resistor and another path with five 6Ω resistors in series.
• Calculate the series path resistance: 5 × 6Ω = 30Ω.
• Compute the parallel equivalent: 1/R = 1/6 + 1/30 = (5 + 1)/30 = 6/30 = 1/5, so R = 5Ω.

Why B is correct:

• Parallel resistors follow 1/R_eq = Σ(1/R_i), yielding exactly 5Ω for 6Ω and 30Ω branches.

Why the others are wrong:

• A: 3Ω assumes only two resistors in parallel, overlooking the series path.
• C: 7.2Ω results from incorrectly combining as 12Ω // 18Ω (two and three in series).
• D: 18Ω treats three resistors in series, ignoring all parallel connections.

Final answer: B