Vo=Vin * R1/(R1+R2)
Vin==> >----
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R1 = [10K]
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----------------------------> Vo
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R2 = [5k]
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GND
Let Vin = 13.5Vdc
Let Vo = 4.5V dc
Let R1 = 10k
Solve for R2:
Then
Vo= 4.5V = 13.5V * 10k / (10k +R2)
=[ 13.5R2/(10k+R2) ] = 4.5V
4.5(10k +R2) = 13.5R2
45k + 4.5R2 = 13.5*R2
45k= (13.5-4.5)R2
45k = 9R2
R2 =5k
Voltage divider to output 4.5Vdc with input of 13.5Vdc = 10k resistor connected to Vin (13.5V battery), 5k resistor connected to GND. Vout of voltage divider taken in the middle where the 10k resistor connects to the 5k resistor.