Three resistors with values of 1 k Ω, 5 k Ω, and 3 k Ω, respectively, are connected in series with a fourth resistor of unknown value. The applied voltage is 120 V and the current flow is 5 mA. What is the resistance value of the unknown resistor?
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15 kΩ
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8 kΩ
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4.5 kΩ
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3.2 kΩ