To do this problem, we must first distribute the 13 and 14 into the parenthesis.
13(9−6m)+14(12m−8)
117 - 78m + 168m - 112
To combine like terms, we can add/subtract terms that have an "m" together and then we can add/subtract terms that do not have "m" together.
117 - 112 = 5
and
168m - 78m = 90m
So our final sum is 5 + 90m
