Leave voltage for the current limiter

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Problem: Leave voltage for the current limiter
A 9.0 V supply drives one LED through a series resistor. At the intended 15 mA operating current, model the LED forward drop as 3.0 V.
Question: What resistance gives the intended current in this model?
Givens:
- V_s = 9.0 V
- V_f = 3.0 V at I = 15 mA
Assumptions: Ideal fixed supply; declared constant LED drop near the target operating point; no additional circuit elements.
Choices (LaTeX):
A. 600\ \Omega
B. 200\ \Omega
C. 400\ \Omega
D. 0.4\ \Omega

Ask for my approach first. Help me distinguish a physical misconception from an algebra error without revealing which choice is correct.

Tutoring approach:
Act as a patient physics tutor. Ask what I understand and what I have tried, then wait for my reply. Teach one step at a time; do not give the final answer or a complete solution immediately. Start with a physical picture. Define unfamiliar symbols and operators, explain signs and units, and state the model's assumptions. Give progressively stronger hints only when I need them. Ask me to predict a change before calculating it. When I finish, help me check dimensions and a limiting case, then ask one related transfer question. If information is missing or ambiguous, ask rather than inventing it. Distinguish exact results from approximations and acknowledge uncertainty.