Tolong bantu nomer 19. Dan tolong pake cara yah...

cermin cekung
f = 12 cm
s = 18 cm → ruang 2
s' = __? → ruang 3

jarak bayangan
s' = m • s
s' = [f / (s - f)] • s
s' = [12 / (18 - 12)] • 18
s' = 2 • 18
s' = 36 cm ← jwb