Problem $1\mathrm{.}4$ Compute the extensional viscosity $\frac{?}{\text{b}\text{a}\text{r}}({)}_b-=\frac{{}_{}-{}_{zz}}{{}^{}}$ in a biaxial extensional

flow for a Newtonian fluid with shear viscosity $$ and where del$\frac{v_x}{d}$elx$=$del$\frac{v_y}{d}$ely$={}^{}$ is the rate

of stretch. Show that $\frac{?}{\text{b}\text{a}\text{r}}({)}_b$ is six times the shear viscosity $.$