Output impedance of a voltage divider with DC bias
The output impedance is not affected by the DC bias.
Treat the DC supply as a short circuit.
The output impedance is all three resistors in parallel - 3.6k//8.3k//1meg.
The input resistance is then just the parallel impedance of the 8.3k and 3.6k resistors in series with the 1 megohm input resistor.
In practice, the input impedance would normally be considered to be just 1 megohm because the 8.3k//3.6k is significantly less than 1% of the input resistor and unless precision resistors are used will be in error by less than the tolerance of the resistors.
Similarly, for the output impedance, you can ignore the 1megohm input resistance as it will have a very minor effect.