3x + 3y = 10

-9 - 9 = - 30

Well if your looking for x and y in this situation you won't have number values as your answer, instead you will have a equation.

3x+3y=10

to find x: you have to get x by itself

3x=10-3y

x = (10-3y) / 3

or x = (10/3) - y

to find y: you have to get y by itself

3y=10-3x

y = (10-3x) / 3

or y = (10/3) - x

I hope this is what you're looking for ...