If x+9-6y+3-4x=12-3x-18, what is the value of 3y

Start by combining like terms on each side

-3x - 6y + 12 = -3x - 6

Adding positive 3x to both sides eliminates the x terms

-6y + 12 = -6

Subtract 12 from each side

-6y = -18

Divide both sides by -6

y = 3

So, to solve for 3y, substitute 3 for y

3y = 3(3) = 9

-3x - 6y + 12 = -3x - 12
First we just clean up the clutter (gather like terms)
we see if we add 3x to both sides the x's disappear.

-6y + 12 = -12
therefore:
solve:
-6y = -24
now you can either solve for y and then multiply by 3 or take a short cut and just divide by -2
3y = 12