Sorry I still have so many questions.

similar to simplifying equations, we can add and subtract things to both sides in inequalities.

so for this inequality, let's start by adding x to both sides.

$2x + x - 5 \le 12$

now let's add five to both sides.

$3x \le 12 + 5$

$3x \le 17$

let's divide both sides by 3.

$x \le \frac{17}{3}$

so, in interval notation, the answer would be:

$(-∞, \frac{17}{3}]$

hope this helped! please let me know if you are confused about anything i did :)