hiii,

Here is the solution to the question

Distance between object and image = 10 cm

Magnification = height of image / height of object =  v/u

M= 1/4 (given)
m= v/u =1/4
u = 4v

u-v = 10cm
so,
4v-v = 10 cm
v= 10/3 cm
hence u =40/3 cm

now applying the lens formula

1/f = 1/v -1/u
= -3/10 + 3/40
= - 4.4 cm

therefore the focal length is -4.4cm

I hope you understand the solution.
Feel free to revert back for any queries.

Thank you!!!