You haven't provided the choices, therefore, I cannot provide an exact answer. However, I will help you with the concept.
For an order pair to be a solution to a system of equations, it has to satisfy BOTH equations. If it satisfies only one equation of the system or satisfy neither of the equations, the, it is not a solutions
Examples:
System 1:
x = y + 1
2x + 3y = 7
Let's check (2,1)
2 = 1 + 1 ........> equation 1 is satisfied
2(2) + 3(1) = 7 ......> equation 2 is satisfied
(2,1) is a solution to this system
System 2:
y = x + 3
y = x - 1
Let's check (2,1):
1 ≠ 2 + 3 ........> equation 1 isn't satisfied
1 = 2 - 1 ..........> equation 2 is satisfied
(2,1) isn't a solution to this system
System 3:
2y = 9 - 3x
3x + 2y = 9
Let's ceck (2,1):
2(1) ≠ 9 - 3(2) ..........> equation 1 isn't satisfied
3(2) + 2(1) ≠ 9 .........> equation 2 isn't satisfied
(2,1) isn't a solution to this system
Based on the above, all you have to do is substitute with (2,1) in the system you have and pick the one where both equations are satisfied
Hope this helps :)