How can I simplify this expression without getting confused?

[Femme_physics]

My basic math is failing me again :(


My attempt to simply:
http://imageshack.us/photo/my-images/209/hw2q.jpg/

My teacher's attempt:



Ignore the difference in notation. He writes || which signifies (A x B) / (A + B) = A || B

And yes I'm aware there is more to simplify but I fail to follow him on the first step

 

[haruspex]

I take it R, S and C are three separate variables.
In $\frac{\frac{R}{SC}}{R+\frac1{SC}}$, multiply top and bottom by SC.

 

[Femme_physics]

Ahh...thank you, I should've seen it!