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With the values shown in kinjalgp's schematic (above), the output will actually be 1.2*Vin+4.8, when what we want is 1.0*Vin+6. You need to change the resistor which goes between the 6 volt divider and pin 3 to 5k in order to get the correct transfer function.
You will not be able to measure 6v on the voltage divider unless Vin is disconnected. This circuit also puts a 20k load on Vin, which may or may not be acceptable.
You can eliminate one resistor by replacing the 5k resistor mentioned above with a short circuit (zero ohms) and making the two resistors in the 6 volt divider equal 20k each, as below.