To find Y, your equation will look like y=(answer)
Start by COMBINING like terms-in this case, the "y's" 9y and 3y
Which will give you a=12y
Next, you want to get y by itself, so you need to DIVIDE by 12 (don't forget that you have to divide on both sides
a/12=12y/12
Your "12"s cancel out, leaving a/12=y and to make it consistent with the question and e format of linear equations: y=a/12