Answer:
a=1
Step-by-step explanation:
What your going to do first is subtract the 3a to 6a,since they have the same variable and you want be able to get the a to be alone.
Now your equation will be 3a+9=12
From here you subtract the 9 to the 12
Now your equation will look like this
3a=3
Now divide the 3 and you will get a=1
Hope this helps :)
