Answer:
Graph C
Explanation:
Graph A (-3, -2) (0, 7)
3(7) + 9(0) = 21
21 = 21 ✓
3(-2) + 9(-3) = 21
-6 - 27 = 21
-33 = 21 ✖
Graph B (0, -7) (3,2)
We know from above that (0, 7) is a point on the line 3y + 9x = 21, therefore point (0, -7) cannot be on that line.
3(2) + 9(3) = 21
6 + 27 = 21
33 = 21 ✖
Graph C (0, 7) (3, -2)
We know from above that (0, 7) is a solution.
3(-2) + 9(3) = 21
-6 + 27 = 21
21 = 21 ✓
Since both points on graph C is a solution to the equation of the line given, it is the answer (looking at graph D is not necessary unless you want to double check your answer).