I am not sure if I understand the question that clearly but if what I think is correct is that you need to prove that 2 and 1 are a system of equations for the following equations so this is how you do that:
With the coordinates (2,1) 2 will be x and 1 will be y because when dealing with coordinates (x,y) is how they are set up.
Next you substitute into the equations and solve:
(2) + 3(1) = 5 and 1 = -(2)+3
So now you find if the equations are true
2 + 3 = 5 so (2,1) is a solution for this equation
-2 + 3 = 1 so (2,1) is also a solution for this equation
So in conclusion (2,1) is a solution of the system of equations
Hope this helps :)
