Chapter 1 - Some Basic Concepts of Arithmetic and Algebra - 1.5 - Use of Properties - Problem Set 1.5 - Page 34: 75

$180$

Combining like terms, the given expression, $ 5x-9xy+3x+2xy ,$ simplifies to \begin{array}{l}\require{cancel} (5x+3x)+(-9xy+2xy) \\\\= 8x-7xy .\end{array} Substituting $ x=12 $ and $ y=-1 ,$ the resulting expression above evaluates to \begin{array}{l}\require{cancel} 8(12)-7(12)(-1) \\\\= 96+84 \\\\= 180 .\end{array}