Question

Which ordered pair is a solution to the equation 3x-3y=21

Answer 1

The equation can be simplified: x-y=7
So y=x-7. So only answer option 2 fits the equation (5,-2)

Answer 2

The answer would be (5, -2). This is because when you plug in the respective values in for x and y into the equation 3x - 3y = 21, you get 21, which is the desired answer.
3x - 3y = 21
3(5) - 3(-2) = 21
15 + 6 = 21
21 = 21 
Hope this helped!