How to simplify a linear equation?

Question

Mathematics

Good day to all.
There is a linear equation for which the result of my solution is not correct.
Therefore, it was decided to use the online service.
In the picture, the result of solving the equation using this service (the result is not final):

I understand how they derived the answer from the simplified equation.
I don't understand the third step. How did they simplify the equation to this form?

Please tell me the simplification algorithm in this case.
Thank you.

Answer 1

Answer 2

Addition and subtraction of fractions, 5th grade of high school.