Hi there!
No, it is not the solution to the equation 3x - 3y = 21
They give us (12, -5). Twelve represents x and -5 represents y.
So, all we have to do is plug them in.
3(12) - 3(-5) = 21
36 + 15 = 21
51 = 21
See... they are not equal because (12, -5) is not the solution of the equation.
Best of luck with your studies!
Please let me know if you have additional questions about my answer.