The best thing to do is get this into a non-denominator form as soon as possible.
[tex]\frac{2}{3} =\frac{x}{12}[/tex]
multiply both sides by 12
[tex]12*\frac{2}{3} =12*\frac{x}{12}[/tex]
Notice that 3 can be divided out of 12
[tex]4*3*\frac{2}{3} = x[/tex]
Simplify and solve
[tex]4*2 = x\\8=x[/tex]
The value of x is 8
