tolong jawab + cara ya makasih :)

Diket:
F=20 cm
S=60 cm

Ditanya: s'??

Jawab:
1/f = 1/s + 1/s'
1/20 = 1/60 + 1/s'
1/20 - 1/60 = 1/s'
3/60 - 1/60 = 1/s'
2/60 = 1/s'
S' = 60/2
S' = 30 cm (C)

Semoga membantu....^^