Answer
$\left[ 3,\infty \right)$
Work Step by Step
Using the properties of inequality, the expression $
0.8x+0.6x\ge4.2
$ simplifies to
\begin{array}{l}
10(0.8x+0.6x)\ge(4.2)10
\\
8x+6x\ge42
\\
14x\ge42
\\
x\ge3
.\end{array}
In interval notation, the solution set is $
\left[ 3,\infty \right)
$.
