Chapter 1 - Some Basic Concepts of Arithmetic and Algebra - 1.5 - Use of Properties - Problem Set 1.5 - Page 34: 60

$2m-8$

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}