Is 3y+x=-20 in standard form?
The equation 3y = -x - 20 in standard form will be x + 3y = -20. You can visit the site http://www.mathsisfun.com/algebra/standard-form.html to get more details on how you work the equation out.
go to google
Isolate the variables and remember what you do to one side do to the other.
Mung is right.