The answer is going to be x=28
Here is how I did it:
You first need to subtract it first
6x/7+15-8=31
6x/7+7=31
you have to find the common denominator
6x/7+7=31
6x/7+7*7/7=31
Multiply all the terms by the same value to eliminate fraction denominators
7(6x+49)/7=7*31
6x+49=7*31
Multiply the numbers
6x+49=7*31
6x+49=217
Subtract 49 from both sides
6x+49=217
-49 -49
Now theres 6x=168
Divide both sides
6x=168
—- —-
6 6
Simplify
x=28 is your answer