Two resistances are connected in two gaps of a metre bridge. The balance point is 20 cm from the zero end. A resistance of $15 \Omega$ is connected in series with the smaller resistance, then the null point shifts to 40 cm. The value of the smaller resistance is:

$3 \Omega$ $6 \Omega$ $9 \Omega$ $12 \Omega$

$9 \Omega$

The correct answer is Option (3) → $9 \Omega$