Concept of common −ion will be applicable for OH− group.
Al(OH)3⇌S Al3++(3s+0.2)3(OH−)
Ksp for Al(OH)3=2.4×10−24=s(3s+0.2)3
Looking at Ksp, it is clear that s will be much lesser than 0.2.
Or, s≪0.2
s×(0.2)3=2.4×10−24⇒s=2.4×10−24/0.008
or, s=3×10−22