tolong dijawab ya kaka pleaseeee ..

panjang bayangan = 15 x 2
= 30 cm

1/f = 1/s + 1/s'
1/f = 1/15 + 1/30
1/f = 2/30 + 1/30
1/f = 3/30
f = 30/3
f = 10 cm