4.91 An LED is forward-biased by a 3-V battery through a resistor. Find the resistor value required to sustain
(a) 10 mA through a green LED at 2.2 V forward voltage drop.
(b) 10 mA through a red LED at 1.8 V forward voltage drop.
(a) 80 Ω; (b) 120 Ω
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