Use addition or substitution to find the value of y for this set of equations. 12x - 5y = 30 y = 2x - 6

So we cant do anything until the 'y' in the 2nd problem is by the 2x. So after we move the 2x over the equation will look like this, "-2x+y=-6."
Now that that is set up we can make our equation.
(12x+5y=30) - (-2x+y=-6) 

We have to multiply the second equation by -6 in order to cancle out the X's. That comes out to (12x-6y=36)

Now the equation looks like (12x+5y=30) - (12x+6y=36)

After you subtract you have (-y=-6)

divide by (-1) and you're left with y=6