Solving for x on 3x - 2y = -39:
First, we must add 2y to both sides.
3x - 2y + 2y = -39 + 2y
3x = 2y - 39
Next, we divide both sides by 3.
3x/3 = 2y - 39/3
Answer: 2/3y - 13
Solving for y on x+3y=31:
First, we must add -x to both of the sides.
x + 3y + -x = 31 + -x
3y = -x + 31
Next, we must divide both sides by 3. (Like last time.)
3y/3 = -x + 31/3
Answer: y = -1/3x + 31/3
I hope this helps! (And what you're looking for! :>)