Question

if have three resistance 6ohm 6ohm 6ohm and the answer is 9. how​

Answer 1

See you can get 9 ohm using three 6 ohm resistor if you connect 2 resistance in parallel and the resulting circuit in series with the third one.

$\frac{1}{Rp} = \frac{1}{6} + \frac{1}{6}$

$\frac{1}{Rp} = \frac{2}{6}$

$Rp = 3 \: ohm$

$Req \: = rp + 6$

$Req \: = 3 + 6$

$Req = 9 \: ohm$