Hi Leela R.
What exactly is your question regarding
2x-30+3x+15=x+3y
5x -15 = x + 3y
5x -x - 15 = x - x + 3y
4x - 15 = 3y
Divide both sides of the equation by 3
(4/3)x - 5 = y
The above put your line in Slope Intercept Form
I hope this is useful otherwise more information is needed about what the specific question is.