$8\mathrm{.}9$ Drugs are infused into an isolated solid tumor via

a constant infusion pressure $p_0.$ There is no blood and

lymph circulation in the tumor, and the pressure at the

surface of the tumor is equal to zero. Assume that the

shape of solid tumors is spherical, the radii of the tumor

and the fluid cavity are a and $,$ respectively, and the

hydraulic conductivity in tumors is K$.$ Determine

$($a$)$ the pressure and velocity profiles in the tumor at

the steady state and

$($b$)$ the infusion rate.