What is the use of Parentheses?

I'm not good at maths and I don't know what theory of maths, if any, I'm using. Sorry.

I get confused to the previous questions "9÷3(6×4÷8)"
I personally think that 9 / 3(6×4÷8) means 9 divided by 3 times of what it is attached.
It means 3 is not a number but a correlated / common factor / coefficient / distributing factors.(something like that)

And it doesn't mean a fraction of 9 over 3. It becomes "9 over 3 times of what it is attached". because the verb is missing it is not a complete questions/sentence. (Sorry I am using a stupid way to think.)

And my teacher taught me to write units in the questions at the very beginning.
e.g. [ 9 ] km / [ 3(6x4÷8) ] hrs = 1km/hrs . The brackets are useless without the units and it becomes 9÷3(6×4÷8).

In other way, it is just A divided by B. and math symbols are to separate things with different meanings.(distance, time, etc.) Is there a theory? I'm not sure.

and 9 / 3 x (6×4÷8) just means 9 divided by 3 times the remain or 9 over 3 times the remain.

So, My approach is :
9 ÷ 3( 6 × 4 ÷ 8 )

= 9 ÷ [( 6 × 4 ÷ 8 ) +( 6 × 4 ÷ 8 ) +( 6 × 4 ÷ 8 )] (3 times of what it is attached)

= 9 ÷ [3 x ( 6 × 4 ÷ 8)] [work as a whole, 3 is describing the times of "( 6 × 4 ÷ 8 )" ]

= 9 / ( 3 x 3)

= 9 / 9

=1

What do you guys think? I think A(B) = (AxB). And thanks for reading.