Answer:
the answer is B) 12a+6b
Step-by-step explanation:
3+9=12 so 3a+9a=12a,
7-1=6 so 7b-(1)b=6b
R + g + b = 50
r = b + 6
g = b - 4
(b + 6) + (b - 4) + b = 50
3b + 2 = 50
3b = 50 - 2
3b = 48
b = 48/3
b = 16 <=== 16 blue marbles
r = b + 6
r = 16 + 6
r = 22 <=== 22 red marbles
g = b - 4
g = 16 - 4
g = 12 <=== 12 green marbles
-3, 8
-2, 7
-1, 6
0, 5
1, 4
2, 3