Question

Show how would you join 3 resistors each of 9ohms so that the equivalent resistance is 6 ohms

Answer 1

the combination of 2 resistance (say A and B ) in series

put that combination in parallel with a other resistance (say C)

resulting resistance of combination AB = 9+9=18ohm

it is in parallel with another resistance

$\frac{1}{resistance} = \frac{1}{18} + \frac{1}{9}$
resistance total = 6

Answer 2

The first 2 resistors when connected in series and the third one when connected in parallel with them , then the answer will be 6, according to your question.