Relative angle of twist between ends of the shaft

[cherry]

TL;DR Summary: A 10-kW engine drives a solid round steel shaft 1 m long by means of a V belt and pulley at the midpoint of the shaft. At one end of the shaft 7 kW is removed and at the other end 3 kW is removed. The shaft diameter is 15 mm and it operates at 1000 rpm. Assuming that no power is lost in the V-belt drive, determine:
a) the relative angle of twist between the ends of the shaft
b)the maximum shear stress in the shaft

I am unsure about question 4a especially regarding my phi equation.
I set the L = 0.5 m as I had interpreted the question to say that the shafts are twisted from the midpoint.
However, shoud I have used L = 1 m instead?

Thanks!

 

[Baluncore]

However, shoud I have used L = 1 m instead?

No. The length of shaft from the input torque to the output torque is 0.5 m on each side.
You show the numbers in the equation, but not the equation you will use, before you insert the numbers.