Chapter 2 - Equations, Inequalities, and Problem Solving - 2.6 Solving Inequalities - 2.6 Exercise Set - Page 135: 81

$x\gt-4$

Using the properties of inequality, the solution to the given inequality, $ 2.1x+43.2\gt1.2-8.4x ,$ is \begin{array}{l}\require{cancel} 2.1x+8.4x\gt1.2-43.2 \\\\ 10.5x\gt-42 \\\\ x\gt-\dfrac{42}{10.5} \\\\ x\gt-4 .\end{array}