Solving "layered" equations for a single variable

I'll start off by saying I'm new to MathCAD, and I'm pretty sure this is just a matter of discovering the proper syntax.

I am trying to solve a fluid flow problem where the flow splits through two paths, of different lengths and diameters.

My process goes like this:

1. define required dimensions, flow characteristics, and fluid properties
2. calculate simple parameters
3. guess one parameter (V2)
4. solve for multiple parameters based on initial guess of V2
5. satisfy a relationship between pressure drops by iterating on V2

The problem, I think, is that V2 shows up on multiple "levels" in my pressure drop equations.

If Pd2 is a function of V2, and a function of f2

and f2 is a function of R2

and R2 is a function of V2

How do I write this out? Pd2(V2,f2(R2(V2))):= ...

Do I have to spell out the whole chain every time I refer to f2?

Do insead have to replace f2 in my Pd2 equation with an expression that is only in terms of V2?

I attached the file for an easier read. Currently it doesn't tell me there is an error, which bugs me.

Thanks