Elementary Algebra

$2m-8$
Using the Distributive Property and then combining like terms, the given expression, $5(m-10)+6(m-11)-9(m-12) ,$ simplifies to \begin{array}{l}\require{cancel} 5m-50+6m-66-9m+108 \\\\= (5m+6m-9m)+(-50-66+108) \\\\= 2m-8 .\end{array}