Chapter 1 - Introduction to Algebraic Expressions - 1.8 Exponential Notation and Order of Operations - 1.8 Exercise Set - Page 67: 119

$-2x-f$

Using order of operations, the given expression, $ \{x-[f-(f-x)]+[x-f]\}-3x $, simplifies to \begin{array}{l}\require{cancel} \{x-[f-f+x]+[x-f]\}-3x \\\\= \{x-[x]+[x-f]\}-3x \\\\= \{x-x+x-f\}-3x \\\\= \{x-f\}-3x \\\\= x-f-3x \\\\= -2x-f .\end{array}