Question

show how you would connect 3 resisters, each of resistance 6 ohm, so that the combination has a resistance of::

9 ohm

4ohm

Answer 1

for 9 ohm two resistor should be in parallel and connected in series with third...
its not possible to connect to get 4 ohm...

Answer 2

For getting 9 ohm as equivalent resistance, connect 2 in parallel and 1 in series.
For getting 4 ohm as the equivalent resistance, connect 2 in series and 1 in parallel.