Distance between the objective mirror and the secondary mirror, d=20mm
Radius of curvature of the objective mirror, R1=220mm
Hence, focal length of the objective mirror, f1=R1/2=110mm
Radius of curvature of the secondary mirror, R2=140mm
Hence, focal length of the secondary mirror, f2=R2/2=70mm
The image of an object placed at infinity, formed by the objective mirror, will act as a virtual object for the secondary mirror.
Hence, the virtual object distance for the secondary mirror, u=f1−d=110−20=90mm
Applying the mirror formula for the secondary mirror,
1/v+1/u=1/f2
⇒v=315mm
Hence, the final image will be formed 315mm away from the secondary mirror.