"Solve for x" means get an equation that says " X = something ". It has nothing but X all alone on one side, and the other side tells exactly what X is equal to.
How do you get such an equation ?
-- Take what they gave you in the question.
-- Do anything you want on one side of it, to get X all by itself on that side.
BUT . . .
-- Whatever you do to one side, you must immediately do the same thing on the other side.
Here's how that goes:
Given in the question: -1 = (5 + X) / 6
Multiply each side by 6 : -6 = 5 + X
Subtract 5 from each side: -11 = X
And there you are. It's over almost as soon as it started.