Focal length =‌

1

P

=‌

1

4

=0.25m or 25‌cm. It is a convex lens as power and focal length are positive.Focal length, f=+25‌cm
Object distance, u=−50‌cm
Image distance, v= ?
Image height, I= ?
Using lens formula, ‌

1

f

=‌

1

v

−‌

1

u

‌

1

25

‌=‌

1

v

−‌

1

(−50)

‌

1

v

‌=‌

1

25

−‌

1

50

v‌=+50‌cm
Also, magnification, m=−‌

v

u

Hence, ‌‌m=‌

(50)

−(50)

=−1
Hence, image is formed at 50‌cm in front of the lens. The image is of the same size as the object as magnification is 1 . The negative magnification shows that image is inverted.