Chapter 1 - Introduction to Algebraic Expressions - 1.8 Exponential Notation and Order of Operations - 1.8 Exercise Set - Page 67: 117

$-5t-6r+21$

Using order of operations, the given expression, $ 5t-\{7t-[4r-3(t-7)]+6r\}-4r $, simplifies to \begin{array}{l}\require{cancel} 5t-\{7t-[4r-3t+21]+6r\}-4r \\\\= 5t-\{7t-4r+3t-21+6r\}-4r \\\\= 5t-\{10t+2r-21\}-4r \\\\= 5t-10t-2r+21-4r \\\\= -5t-6r+21 .\end{array}