Answer:
B. 149
Explanation:
If the students have already filled 139 balloons with air and are going to use all the bags. They would need to fill 149 more balloons.
The first step would be to find the total number of ballons by calculating 12x24 which will give you 288.
From here you would need to subtract the number of ballons that are already filled with air from the balloons that remain which would be 288-139. This would give you a total of 149 balloons that still need to be inflated.