Answer:
C. 4x + y = 21
Step-by-step explanation:
X + 2y = 21
A. 4x + 6y = 64
B. 2x + y = 36
C. 4x + y = 21
D. -3x + 4y = 33
E. 3x + 2y = 28
x = 3
y = 9
X + 2y = 21
3 + 2(9) = 21
3 + 18 = 21
21 = 21
A. 4x + 6y = 64
4(3) + 6(9) = 64
12 + 54 = 64
66 is not = 64
B. 2x + y = 36
2(3) + 9 = 36
6 + 9 = 36
15 is not = 36
C. 4x + y = 21
4(3) + 9 = 21
12 + 9 = 21
21 = 21