A cell phono that is 890 cm tall is placed in front of a con

A cell phono that is 8.90 cm tall is placed in front of a convex mirror the imago of the phono is 7.80 cm tall and is located 14 8 cm from a mirror What is the mirror\'s local length? -120 cm -105 cm + 16.9cm -13.0 cm + 120 cm

focal length of convex mirror is, f < 0, or it has negative sign
d\' = -14.8 cm,
magnification: = -d\'/d = h/h0

14.8/d =7.8/8.9
d = 16.9 cm
focal length of mirror: