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 answer: x = 2, y = 5
Hope this helps!