[tex] - 15 + 8x = x + 3 \\ 8x - x = 3 + 15 \\ 7x = 18 \\ \\ x = \frac{18}{7} \\ \\ x = 2.571[/tex]
We put the unknown on one side, and the other end is empty of the unknown , When it turns to the other side, its sign changes.
As for the number with the unknown, it becomes the denominator with the number without the unknown.
I hope I helped you^_^
