How do you solve 3x+y=-4
x=2/3y in substitution method

How do you solve 3x+y=-4
x=2/3y in substitution method
all you have to do is in the first equation (or whichever one seems easier) put in what the second equation says x is equal to.

For your example, if you decide to use the first one as your "working" equation you would use the second one to substitute in for the x in the first equation.

so your working problem would then look like this:

3(2/3y) + y = -4 and now you can solve for y

Once you have the value for y, you then put that y-value into one of the equations (I always pick the one that will give me the easier math) and then you solve for x because that is the only variable!

Yes, it's a called a "simultaneous equation".