# How to know which efficiencies to take into account when calculating power of a certain part of a power transmission system?

I have an example which I am not certain about:

So It consists of a friction wheel, whose power $$P_{fw}$$ we know. The power is used to power the driven machine $$Dm$$ on a shaft that lies on 2 bearings, $$A$$ and $$B$$. That shaft is connected to a spindle via the clutch $$Cl$$. The spindle lies on 2 bearings $$C$$ and $$D$$ and is used to move $$m$$

the bearings, the clutch and the spindle all have their coefficients of efficiency: $$\eta_{A}, \eta_{B}, \eta_{Cl}, \eta_{C}, \eta_{D}, \eta_{sp}$$

I want to know the power on the driven machine DM. My question is which of these coefficients do I take into account? I'm pretty sure I need $$\eta_{A}$$ and $$\eta_{B}$$, but I don't know abut the others.

So my solution would be $$P_{dm}=P_{fw}*\eta_{A}*\eta_{A}$$ but I am not certain about it. Please explain if this is correct and why/why not.