Question 259077
We are not trying to reduce 6/12 nor 9/18 ! 
6/12 does equal 1/2 and 9/18 does equal 1/2 !
But that is not the question!
The question is how do you go from 6/12 to 9/18.
6*? =9
and 12*?=18

First let's check the teacher's answer
Remember that 1.5 =1 1/2 = 3/2

6*3/2/12*3/2=9/18
18/2/36/2=9/18
The teacher is right.
We can do it with 1.5 too

6*1.5/12*1.5=9/18

So now to solve the question
9/6=3/2=1.5
18/12=3/2=1.5
(6/12)*(1.5/1.5)=9/18
{{{(6/12)*(1.5/1.5)=9/18}}}