Question

plans answer fast it's urgent​

Answer 1

m=+3 ; m=-3

when m=+3

   m=-v/u

   3=-v/u

   v=-3u

1/f=1/v+1/u

-1/20=-1/3u+1/u

1/u=1/3u-1/20

1/u=(20-3u)/60u

60=20-3u      [u cancels in the denominator]

-3u=60-20

-3u=40

u = - 40 / 3

u = - 13.33 cm

when m=-3

repeat the same steps when m = +3

then u=-80/3= 26.67 cm