pakai caranya,thanks ya

1/f = 1/so + 1/si
-1/20 = 1/40 + 1/si
-1/20 - 1/40 = 1/si
-2/40 - 1/40 = 1/si
-3/40 = 1/si
si = -40/3 cm
si = 40/3 cm di depan lensa

M = si/so
= [-40/3 / 40]
= 40/120
= 1/3 kali

M = hi/ho
1/3 = hi/75
1/3 × 75 = hi
25 = hi
hi = 25 mm (a)