30m-7
18m-7+12m
12(m+n)
Not unless m = n.
12m + 3n - 6m + 7n6m + 10n
An algebraic expression
12m + 2n - 3m + 11n = 9m + 13n
-6
If you mean: 12(3+m) then it is the same as 36+12m
m(12 + 7n)
m2 + 12m + 20 = ( m + 2)(m + 10)
12m + 9n - 4 - 10m + 6n = 2m + 15n - 4
4(3m - 4)