The first step to solving this is to collect the like terms in this equation,, which are all the numbers with an x variable attached to them.
8.5x = -25.5
Now all you need to do to find x is divide both sides of the equation by 8.5
x = -3
This means that in order to make this equation true,, x must be -3.
Let me know if you have any further questions
:)