3x-3y=-9 and 2x +y =9 solve for both x and y

You can solve for x and y by using the system of equations. That is when one term of one equation is opposite of its corresponding term in the other.

3x - 3y = -9
2x +  y = 9

You can get y to be the opposite of -3y by multiply the second equation by 3

3x - 3y = -9
6x + 3y = 27

Combine the equations, -3y and 3y cancel each other out

9x = 18
x = 2

Now plug the value of x back into one of the original equations

3x - 3y = -9
3(2) - 3y = -9
6 - 3y = - 9
-3y = -15
y = 5

To check you can plug both values into the other equation
2x + y = 9
4 + 5 = 9

Final x = 2, y = 5
Hope this helps!