Boyong,

The subject line of your email was "what is the right answer?,9 or 1". The real question is "Who would write such a statement?" It looks like it is written with a deliberate attempt to be confusing. Mathematicians take great care in ensuring that what they write is clear and unambiguous. If it were written (6/2)(1+2) then you perform the operations inside the parentheses first giving $3 \times 3 = 9.$ If it were written 6/(2(1+2)) you would again perform the operations inside the parentheses first giving $6/6 = 1.$ As it stands it is not clear what is meant.

If this is a textbook problem then the text is probably using the PEDMAS or BEDMAS rule which says to do division before multiplication. In that case you would get an answer of 9.

Harley