Diverging lens forms the image at its focus. The image formed by diverging lens is the object for converging lens.

$\therefore$ Distance of the object from converging lens is $40 \mathrm{cm}$ i.e., object is at double focal point.

$\therefore$ Image forms at double focal point on the other side of the lens.
$\frac{1}{v}-\frac{1}{4}=\frac{1}{f}$
1v-1-40=120
$\frac{1}{v}+\frac{1}{40}=\frac{1}{20}$
$\frac{1}{v}=\frac{1}{20}-\frac{1}{40}=\frac{1}{40}$
$v=40$