The solid steel shaft DF has a diameter of $25mm$ and is supported by smooth bearings at $D$ and $E.$ It is coupled to a motor at $F,$ which delivers $12kW$ of power to the shaft while it is turning at If gears $A,B,$ and $C$ remove $3kW,4kW,$ and $5kW$ respectively, determine the maximum shear stress developed in the shaft within regions CF and BC$.$ The shaft is free to turn in its support bearings $D$ and $E.$