Since the graphic shows you that both angles across from both of the sides are equal we can tell that both sides are equal.
Now to solve for the variable all you need to do is make an equation where both of the sides are equal to each other.
So...8x - 12 = 12x - 18
Now to solve you need to get rid of the constants, or regular numbers. To do this, add 12 to both sides.
So...8x = 12x - 6
Next, you need to move the variable to one side, do this by subtracting 12x from both sides.
So... -6x = -6
Finally, divide both sides by -6 to get what the variable equals.
So...x = 1
Your final answer is both sides equal 1 in.
