Elementary and Intermediate Algebra: Concepts & Applications (6th Edition)

$\left\{ x|x\le4.475 \right\} \text{ or } \left( -\infty, 4.475 \right]$
Using the properties of inequality, the given inequality, $0.4x+5.7\le2.6-3(1.2x-7) ,$ is equivalent to \begin{array}{l}\require{cancel} 0.4x+5.7\le2.6-3.6x+21 \\\\ 0.4x+3.6x\le2.6+21-5.7 \\\\ 4x\le17.9 \\\\ x\le\dfrac{17.9}{4} \\\\ x\le4.475 .\end{array} Hence, the solution is $\left\{ x|x\le4.475 \right\} \text{ or } \left( -\infty, 4.475 \right] .$