First give the unknown a pronumeral. I chose N
Multiply both sides by 12 to get rid of the fraction.
Take all the x terms to one side and the non-x terms on the other side.
Factorise out the x
Divide both sides by what ever was in front of the x (the co-efficent of x)
Now you have x = a fraction with an N on the top and an N on the bottom (along with other stuff)
This can only have a solution if the denominator (bottom) is not equal to 0
forget about the top and put the bottom = 0
solve this new equation
You'll get N= something
That something is what N cannot equal if the original equation is to have a solution.
+118654 
