Chapter 1 - Some Basic Concepts of Arithmetic and Algebra - 1.5 - Use of Properties - Problem Set 1.5 - Page 34: 78

$28$

Combining like terms, the given expression, $ (a+b)-(a-b) ,$ simplifies to \begin{array}{l}\require{cancel} a+b-a+b \\\\= (a-a)+(b+b) \\\\= 0+2b \\\\= 2b .\end{array} Substituting $ b=14 ,$ the resulting expression above evaluates to \begin{array}{l}\require{cancel} 2(14) \\\\= 28 .\end{array}