$($i$)$ Viscous fluid flows between two stationary rigid boundaries

$y=+-h$ under a constant pressure gradient $P=-d\frac{p}{d}x.$ Show that

$u=\frac{P}{2}(h^2-y^2),v=w=0$

$($ii$)$ Viscous fluid flows down a pipe of circular cross$-$section $r=a$

under a constant pressure gradient $P=-d\frac{p}{d}z.$ Show that

$u_z=\frac{P}{4}(a^2-r^2),u_r=u_{}=0$

$($Please specify the boundary conditions for the $2$nd case and use them to prove the expression clearly $)$