please bantuin kakak

pH Al(OH)3 = 9
POH = 14 - 9 = 5
OH¯ = 10¯5

OH¯ = b x M
M = OH¯ / b
= 10¯5/3 = 3.10¯6

Ksp Al(OH)3 ↔Al3+ + 3OH¯
Ksp = 27s⁴
= 27(3.10¯6)⁴
= 2187.10¯²⁴