Answer:
13
Step-by-step explanation:
A bag contains green marbles and blue marbles, 24 in total: g + b = 24
The number of green marbles is 9 less than 2 times the number of blue marbles: g = 2b - 9
Substitute g = 2b - 9 into g + b = 24
2b-9+b=24
3b=24+9=33
b=11
Substitute b = 11 into g = 2b - 9
g=22-9 = 13