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-m^2 - 9m + 3 (the third one)

Step-by-step explanation:

separate the terms and group them with their equivalents (integers:inetgers, variables: variables, etc.) like so:

4m^2   &   -5m^2    = -m^2

-8m      &   -m          = -9m

12         &    -9          = 3

add them all together to get the expression -m^2-9m+3