Answer:
It would be the third one! :)
Step-by-step explanation: Because it says the number of marbles is represented by M then it says he ADDS 8 more to the bag meaning it's addition! :)
m + 8
Explanation:
you start with the original number of marbles, m, and you ADD 8 more to the group.
Original number (m) + 8 more
M = 8
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