How do you solve -5x-6+144?

Using the word 'solve' implies determining the value of $x$. This you can not do as there is no equals sign. You can simplify it to
$- 5 x + \left(144 - 6\right) \textcolor{w h i t e}{\text{ddd") ->color(white)("ddd}} - 5 x + 138$