The correct option is D 20 cm away from lens.
Initially,
Object distance from the lens, u=−40 cm
Image distance from the lens, v=40 cm
Image distance is equal to the object distance. This happens when object is at 2f distance from the lens.
2f=40
f=20 cm
When the object is moved 10 cm towards the lens, new object distance is:
u′=−(40−10) cm
u′=−30 cm
Applying lens formula, the new image distance v′ is
120=1v′−1(−30)
v′=60 cm
Shift in image is:
Δv=v′−v
Δv=60−40=20 cm
Thus, the image shift is 20 cm away from the convex lens.