Answer
0.0017
Work Step by Step
We know: Shear modulus, G= Shear stress/Shear strain.
This is the same as: Shear strain = Shear stress$\div$ Shear modulus
Thus, it follows:
= $\frac{8.5\times10^{6}N/m^{2}}{5.0\times10^{9}N/m^{2}}$ = 0.0017