Equation 6.43 describes the laminar flow of a power law fluid in a tube. Since a power law fluid is defined by the relation $\tau=m \dot{\gamma}^{n}$, rearrange Equation 6.43 to show that the shear rate at the tube wall for a power law fluid is given by $\dot{\gamma}_{w}=(8 V / D)(3 n+1) / 4 n$ where $8 V / D$ is the wall shear rate for a Newtonian fluid.