[tex]\frac{x}{2} + \frac{x}{2} = \frac{8}{12} \\\frac{2x}{2} = \frac{2}{3} \\x = \frac{2}{3}[/tex]
or
[tex]\frac{x}{2} + \frac{x}{2} = \frac{8}{12} \\\frac{x}{2} + \frac{x}{2} = \frac{2}{3} \\\frac{\frac{2}{3}}{2} + \frac{\frac{2}{3}}{2} = \frac{2}{3} \\\frac{1}{3} + \frac{1}{3} = \frac{2}{3} \\\frac{2}{3} = \frac{2}{3}[/tex]