Chapter 1 - Introduction to Algebraic Expressions - 1.8 Exponential Notation and Order of Operations - 1.8 Exercise Set - Page 67: 109

$-7t^3-15t^3-t^2+9t$

Using $a(b+c)=ab+ac$ or the Distributive Property, the given expression, $ -7t^3-t^2-3(5t^3-3t) $, is equivalent to \begin{array}{l}\require{cancel} -7t^3-t^2-3(5t^3)-3(-3t) \\\\= -7t^3-t^2-15t^3+9t \\\\= -7t^3-15t^3-t^2+9t .\end{array}