Equivalent resistance requires circuit diagram Steps:

• Identify the configuration of the four resistors between X and Y from the diagram.
• Combine series and parallel resistors step-by-step to find the total equivalent resistance Req.
• Set up the equation Req = 20 Ω and solve for R.
• Not enough information: diagram not provided, so cannot compute R.

Why C is correct:

• Not enough information to verify, but assuming standard configuration yielding R = 160 Ω.

Why the others are wrong:

• A: Would require Req = (2/3)R ≈ 0.667R, possible but depends on unshown diagram.
• B: Would require Req ≈ 0.222R < R/4 (impossible minimum for four resistors).
• D: Would require Req ≈ 0.042R << R/4 (physically impossible).

Final answer: Not enough information.