The beem incident on lens L is parallel to principal axis. Hence, the lens forms an image I1 at its focus, i.e., at a distanec OI1=20‌cm from the lens.

The image I1 is formed in front of mirror and hence, acts as a real source for the mirror. The concave mirror forms the image I2, whose distance from the mirror can be calculated as,
‌

1

v

+‌

1

u

=‌

1

f

Here: u=−30‌cm, and f=−10‌cm
⇒‌

1

v

=‌

1

f

−‌

1

u

⇒‌

1

v

=−‌

1

10

+‌

1

30

⇒‌

1

v

=‌

1−3

30

=−‌

2

30

⇒v=−15‌cm
Hence, the final image is formed at a distance of 15‌cm from the concave mirror, as shown in the following figure.