finding torque

[freespirit]

the steel diameter shaft is 6' long and its outer diameter and inner diameter are respectively equal to 2.25 in and 1.75 in a) detemine the maximum shearing stress b) using G= 11.2 PSI detemine the corresponding angle of twist of the shaft.

what I have done so far:
d1=2.25
d2= 1.75
L=6'
G= 11.2x10^6

J=pi/2 (d2^4-d1^4)

I know I need to use shearing stress= Tc/J
and fe=TL/JG

How do I find the torque T?

Thanks Debi