(a) When the object is placed between the pole and the focus, then a magnified, virtual and erect image is formed by concave mirror.

When the object is placed between centre of curvature and focus then a magnified, real and inverted image is formed by concave mirror.

(b) For virtual image;
‌

h′

h

‌=−‌

v

u

=3
∴‌‌v‌=−3u
Putting in mirror formula :
‌

1

v

+‌

1

u

=‌

1

f

Or, ‌

1

−3u

+‌

1

u

=‌

1

−12

∴u=−8‌cm
For real image;
‌

h′

h

‌=−‌

v

u

=3
∴‌‌v‌=3u
Putting in mirror formula :
‌

1

v

+‌

1

u

‌=‌

1

f

∴‌‌u‌=−16‌cm
The distance between the two positions is 8‌cm.