How many chiral carbons and optical isomers are there in this carbohydrate?

Question

a) How many chiral carbons are there in this carbohydrate?

b) How many optical isomers does this carbohydrate have ?

....CHO
.....I
H-C-OH
.....I
H-C-OH
.....I
H-C-OH
.....I
CH2OH

the periods i wrote are to hold the bonds where they are supposed to be

Answer 1

There are 3 chiral carbon atoms, there doesn't exists an internal plane of symmetry, so there are 3^2 = 9 optical isomers.

Answer 2

i think the chiral carbons would be 3..but..i think the optimal isomers would be 6..cuz someone told me that for for every chiral carbon, there would be 2 opticacl isomers.