Question

the image of distance object is formed at 30 cm from a concave mirror what is the focal length of the mirror​

Answer 1

1/f=1/v+1/u

1/f= 1/30+0

f= 30 cm

Answer 2

given that it is distant object so probably the object distance u will be infinity

given v=30 cm

f=?

mirror formula

1/f=1/v+1/u

1/f=1/30+1/infinity

f=30 cm

image is formed behind the mirror and is virtual

hope this helps