Jarak bayangannya adalah...

1/s' = 1/f - 1/s
1/s' = 1/2 - 1/3
1/s' = 3/6 - 2/6 = 1/6
S' = 1 × 6 = 6 cm

f = 2 cm
s = 3 cm
s' = ___?

s' = sf / (s - f)
   = 3 cm . 2 cm / (3 cm - 2 cm)
   = 6 cm / 1 cm
   = 6 cm