An elevator control system requires 3 resistors connected in series. The values of the resistors are R1, R2, and R3. The total resistance (RT) is 150 ohms. If R1 = 45 ohms and R2 is twice the value of R1, what is the value of R3 in ohms?
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A
45 ohms
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B
90 ohms
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C
15 ohms
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D
135 ohms