How do you do something like x over 2?

You can use the math formula tool to write it.

x/2        $${\frac{{\mathtt{x}}}{{\mathtt{2}}}}$$

OR you can use the LaTex tool to write it

\frac{x}{2}            $$\frac{x}{2}$$

What exactly do you mean?

 

Like x/2 = 9?

You would just cross multiply leading to x = 9*2 = 18. Another way would be to think about what divided by 2 gives 9.