$3\mathrm{.}5-6$ A solid circular bar of diameter $d=50mm$

$($see figure$)$ is twisted in a testing machine until the

applied torque reaches the value $T=500N*m.$ At

this value of torque, a strain gage oriented at $45$ to the

axis of the bar gives a reading $=339{10}^{-6}.$

What is the shear modulus $G$ of the material?